struct — Interpret bytes as packed binary data Source code: Lib/struct.py This module performs conversions between Python values and C structs represented as Python bytes objects. This can be used in handling binary data stored in files or from network connections, among other sources. It uses Format Strings as compact descriptions of the layout of the C structs and the intended conversion to/from Python values.  Note By default, the result of packing a given C struct includes pad bytes in order to maintain proper alignment for the C types involved; similarly, alignment is taken into account when unpacking. This behavior is chosen so that the bytes of a packed struct correspond exactly to the layout in memory of the corresponding C struct. To handle platform-independent data formats or omit implicit pad bytes, use standard size and alignment instead of native size and alignment: see Byte Order, Size, and Alignment for details.  Several struct functions (and methods of Struct) take a buffer argument. This refers to objects that implement the Buffer Protocol and provide either a readable or read-writable buffer. The most common types used for that purpose are bytes and bytearray, but many other types that can be viewed as an array of bytes implement the buffer protocol, so that they can be read/filled without additional copying from a bytes object. Functions and Exceptions The module defines the following exception and functions:
exception struct.error
Exception raised on various occasions; argument is a string describing what is wrong.

struct.pack(format, v1, v2, ...)
Return a bytes object containing the values v1, v2, … packed according to the format string format. The arguments must match the values required by the format exactly.

struct.pack_into(format, buffer, offset, v1, v2, ...)
Pack the values v1, v2, … according to the format string format and write the packed bytes into the writable buffer buffer starting at position offset. Note that offset is a required argument.

struct.unpack(format, buffer)
Unpack from the buffer buffer (presumably packed by pack(format, ...)) according to the format string format. The result is a tuple even if it contains exactly one item. The buffer’s size in bytes must match the size required by the format, as reflected by calcsize().

struct.unpack_from(format, /, buffer, offset=0)
Unpack from buffer starting at position offset, according to the format string format. The result is a tuple even if it contains exactly one item. The buffer’s size in bytes, starting at position offset, must be at least the size required by the format, as reflected by calcsize().

struct.iter_unpack(format, buffer)
Iteratively unpack from the buffer buffer according to the format string format. This function returns an iterator which will read equally-sized chunks from the buffer until all its contents have been consumed. The buffer’s size in bytes must be a multiple of the size required by the format, as reflected by calcsize(). Each iteration yields a tuple as specified by the format string.  New in version 3.4.

struct.calcsize(format)
Return the size of the struct (and hence of the bytes object produced by pack(format, ...)) corresponding to the format string format.
 Format Strings Format strings are the mechanism used to specify the expected layout when packing and unpacking data. They are built up from Format Characters, which specify the type of data being packed/unpacked. In addition, there are special characters for controlling the Byte Order, Size, and Alignment. Byte Order, Size, and Alignment By default, C types are represented in the machine’s native format and byte order, and properly aligned by skipping pad bytes if necessary (according to the rules used by the C compiler). Alternatively, the first character of the format string can be used to indicate the byte order, size and alignment of the packed data, according to the following table:
Character Byte order Size Alignment
@ native native native
= native standard none
< little-endian standard none
> big-endian standard none
! network (= big-endian) standard none   If the first character is not one of these, '@' is assumed. Native byte order is big-endian or little-endian, depending on the host system. For example, Intel x86 and AMD64 (x86-64) are little-endian; Motorola 68000 and PowerPC G5 are big-endian; ARM and Intel Itanium feature switchable endianness (bi-endian). Use sys.byteorder to check the endianness of your system. Native size and alignment are determined using the C compiler’s sizeof expression. This is always combined with native byte order. Standard size depends only on the format character; see the table in the Format Characters section. Note the difference between '@' and '=': both use native byte order, but the size and alignment of the latter is standardized. The form '!' represents the network byte order which is always big-endian as defined in IETF RFC 1700. There is no way to indicate non-native byte order (force byte-swapping); use the appropriate choice of '<' or '>'. Notes:  Padding is only automatically added between successive structure members. No padding is added at the beginning or the end of the encoded struct. No padding is added when using non-native size and alignment, e.g. with ‘<’, ‘>’, ‘=’, and ‘!’. To align the end of a structure to the alignment requirement of a particular type, end the format with the code for that type with a repeat count of zero. See Examples.  Format Characters Format characters have the following meaning; the conversion between C and Python values should be obvious given their types. The ‘Standard size’ column refers to the size of the packed value in bytes when using standard size; that is, when the format string starts with one of '<', '>', '!' or '='. When using native size, the size of the packed value is platform-dependent.
Format C Type Python type Standard size Notes
x pad byte no value
c char bytes of length 1 1
b signed char integer 1 (1), (2)
B unsigned char integer 1 (2)
? _Bool bool 1 (1)
h short integer 2 (2)
H unsigned short integer 2 (2)
i int integer 4 (2)
I unsigned int integer 4 (2)
l long integer 4 (2)
L unsigned long integer 4 (2)
q long long integer 8 (2)
Q unsigned long
long integer 8 (2)
n ssize_t integer  (3)
N size_t integer  (3)
e (6) float 2 (4)
f float float 4 (4)
d double float 8 (4)
s char[] bytes
p char[] bytes
P void * integer  (5)    Changed in version 3.3: Added support for the 'n' and 'N' formats.   Changed in version 3.6: Added support for the 'e' format.  Notes:  The '?' conversion code corresponds to the _Bool type defined by C99. If this type is not available, it is simulated using a char. In standard mode, it is always represented by one byte.
When attempting to pack a non-integer using any of the integer conversion codes, if the non-integer has a __index__() method then that method is called to convert the argument to an integer before packing.  Changed in version 3.2: Added use of the __index__() method for non-integers.   The 'n' and 'N' conversion codes are only available for the native size (selected as the default or with the '@' byte order character). For the standard size, you can use whichever of the other integer formats fits your application. For the 'f', 'd' and 'e' conversion codes, the packed representation uses the IEEE 754 binary32, binary64 or binary16 format (for 'f', 'd' or 'e' respectively), regardless of the floating-point format used by the platform. The 'P' format character is only available for the native byte ordering (selected as the default or with the '@' byte order character). The byte order character '=' chooses to use little- or big-endian ordering based on the host system. The struct module does not interpret this as native ordering, so the 'P' format is not available. The IEEE 754 binary16 “half precision” type was introduced in the 2008 revision of the IEEE 754 standard. It has a sign bit, a 5-bit exponent and 11-bit precision (with 10 bits explicitly stored), and can represent numbers between approximately 6.1e-05 and 6.5e+04 at full precision. This type is not widely supported by C compilers: on a typical machine, an unsigned short can be used for storage, but not for math operations. See the Wikipedia page on the half-precision floating-point format for more information.  A format character may be preceded by an integral repeat count. For example, the format string '4h' means exactly the same as 'hhhh'. Whitespace characters between formats are ignored; a count and its format must not contain whitespace though. For the 's' format character, the count is interpreted as the length of the bytes, not a repeat count like for the other format characters; for example, '10s' means a single 10-byte string, while '10c' means 10 characters. If a count is not given, it defaults to 1. For packing, the string is truncated or padded with null bytes as appropriate to make it fit. For unpacking, the resulting bytes object always has exactly the specified number of bytes. As a special case, '0s' means a single, empty string (while '0c' means 0 characters). When packing a value x using one of the integer formats ('b', 'B', 'h', 'H', 'i', 'I', 'l', 'L', 'q', 'Q'), if x is outside the valid range for that format then struct.error is raised.  Changed in version 3.1: Previously, some of the integer formats wrapped out-of-range values and raised DeprecationWarning instead of struct.error.  The 'p' format character encodes a “Pascal string”, meaning a short variable-length string stored in a fixed number of bytes, given by the count. The first byte stored is the length of the string, or 255, whichever is smaller. The bytes of the string follow. If the string passed in to pack() is too long (longer than the count minus 1), only the leading count-1 bytes of the string are stored. If the string is shorter than count-1, it is padded with null bytes so that exactly count bytes in all are used. Note that for unpack(), the 'p' format character consumes count bytes, but that the string returned can never contain more than 255 bytes. For the '?' format character, the return value is either True or False. When packing, the truth value of the argument object is used. Either 0 or 1 in the native or standard bool representation will be packed, and any non-zero value will be True when unpacking. Examples  Note All examples assume a native byte order, size, and alignment with a big-endian machine.  A basic example of packing/unpacking three integers: >>> from struct import *
>>> pack('hhl', 1, 2, 3)
b'\x00\x01\x00\x02\x00\x00\x00\x03'
>>> unpack('hhl', b'\x00\x01\x00\x02\x00\x00\x00\x03')
(1, 2, 3)
>>> calcsize('hhl')
8
 Unpacked fields can be named by assigning them to variables or by wrapping the result in a named tuple: >>> record = b'raymond   \x32\x12\x08\x01\x08'
>>> name, serialnum, school, gradelevel = unpack('<10sHHb', record)

>>> from collections import namedtuple
>>> Student = namedtuple('Student', 'name serialnum school gradelevel')
>>> Student._make(unpack('<10sHHb', record))
Student(name=b'raymond   ', serialnum=4658, school=264, gradelevel=8)
 The ordering of format characters may have an impact on size since the padding needed to satisfy alignment requirements is different: >>> pack('ci', b'*', 0x12131415)
b'*\x00\x00\x00\x12\x13\x14\x15'
>>> pack('ic', 0x12131415, b'*')
b'\x12\x13\x14\x15*'
>>> calcsize('ci')
8
>>> calcsize('ic')
5
 The following format 'llh0l' specifies two pad bytes at the end, assuming longs are aligned on 4-byte boundaries: >>> pack('llh0l', 1, 2, 3)
b'\x00\x00\x00\x01\x00\x00\x00\x02\x00\x03\x00\x00'
 This only works when native size and alignment are in effect; standard size and alignment does not enforce any alignment.  See also
Module array

Packed binary storage of homogeneous data.
Module xdrlib

Packing and unpacking of XDR data.    Classes The struct module also defines the following type:
class struct.Struct(format)
Return a new Struct object which writes and reads binary data according to the format string format. Creating a Struct object once and calling its methods is more efficient than calling the struct functions with the same format since the format string only needs to be compiled once.  Note The compiled versions of the most recent format strings passed to Struct and the module-level functions are cached, so programs that use only a few format strings needn’t worry about reusing a single Struct instance.  Compiled Struct objects support the following methods and attributes:
pack(v1, v2, ...)
Identical to the pack() function, using the compiled format. (len(result) will equal size.)

pack_into(buffer, offset, v1, v2, ...)
Identical to the pack_into() function, using the compiled format.

unpack(buffer)
Identical to the unpack() function, using the compiled format. The buffer’s size in bytes must equal size.

unpack_from(buffer, offset=0)
Identical to the unpack_from() function, using the compiled format. The buffer’s size in bytes, starting at position offset, must be at least size.

iter_unpack(buffer)
Identical to the iter_unpack() function, using the compiled format. The buffer’s size in bytes must be a multiple of size.  New in version 3.4.

format
The format string used to construct this Struct object.  Changed in version 3.7: The format string type is now str instead of bytes.

size
The calculated size of the struct (and hence of the bytes object produced by the pack() method) corresponding to format.


struct.calcsize(format)
Return the size of the struct (and hence of the bytes object produced by pack(format, ...)) corresponding to the format string format.


exception struct.error
Exception raised on various occasions; argument is a string describing what is wrong.


struct.iter_unpack(format, buffer)
Iteratively unpack from the buffer buffer according to the format string format. This function returns an iterator which will read equally-sized chunks from the buffer until all its contents have been consumed. The buffer’s size in bytes must be a multiple of the size required by the format, as reflected by calcsize(). Each iteration yields a tuple as specified by the format string.  New in version 3.4.


struct.pack(format, v1, v2, ...)
Return a bytes object containing the values v1, v2, … packed according to the format string format. The arguments must match the values required by the format exactly.


struct.pack_into(format, buffer, offset, v1, v2, ...)
Pack the values v1, v2, … according to the format string format and write the packed bytes into the writable buffer buffer starting at position offset. Note that offset is a required argument.


class struct.Struct(format)
Return a new Struct object which writes and reads binary data according to the format string format. Creating a Struct object once and calling its methods is more efficient than calling the struct functions with the same format since the format string only needs to be compiled once.  Note The compiled versions of the most recent format strings passed to Struct and the module-level functions are cached, so programs that use only a few format strings needn’t worry about reusing a single Struct instance.  Compiled Struct objects support the following methods and attributes:
pack(v1, v2, ...)
Identical to the pack() function, using the compiled format. (len(result) will equal size.)

pack_into(buffer, offset, v1, v2, ...)
Identical to the pack_into() function, using the compiled format.

unpack(buffer)
Identical to the unpack() function, using the compiled format. The buffer’s size in bytes must equal size.

unpack_from(buffer, offset=0)
Identical to the unpack_from() function, using the compiled format. The buffer’s size in bytes, starting at position offset, must be at least size.

iter_unpack(buffer)
Identical to the iter_unpack() function, using the compiled format. The buffer’s size in bytes must be a multiple of size.  New in version 3.4.

format
The format string used to construct this Struct object.  Changed in version 3.7: The format string type is now str instead of bytes.

size
The calculated size of the struct (and hence of the bytes object produced by the pack() method) corresponding to format.


format
The format string used to construct this Struct object.  Changed in version 3.7: The format string type is now str instead of bytes.


iter_unpack(buffer)
Identical to the iter_unpack() function, using the compiled format. The buffer’s size in bytes must be a multiple of size.  New in version 3.4.


pack(v1, v2, ...)
Identical to the pack() function, using the compiled format. (len(result) will equal size.)


pack_into(buffer, offset, v1, v2, ...)
Identical to the pack_into() function, using the compiled format.


size
The calculated size of the struct (and hence of the bytes object produced by the pack() method) corresponding to format.


unpack(buffer)
Identical to the unpack() function, using the compiled format. The buffer’s size in bytes must equal size.


unpack_from(buffer, offset=0)
Identical to the unpack_from() function, using the compiled format. The buffer’s size in bytes, starting at position offset, must be at least size.


struct.unpack(format, buffer)
Unpack from the buffer buffer (presumably packed by pack(format, ...)) according to the format string format. The result is a tuple even if it contains exactly one item. The buffer’s size in bytes must match the size required by the format, as reflected by calcsize().


struct.unpack_from(format, /, buffer, offset=0)
Unpack from buffer starting at position offset, according to the format string format. The result is a tuple even if it contains exactly one item. The buffer’s size in bytes, starting at position offset, must be at least the size required by the format, as reflected by calcsize().


subprocess — Subprocess management Source code: Lib/subprocess.py The subprocess module allows you to spawn new processes, connect to their input/output/error pipes, and obtain their return codes. This module intends to replace several older modules and functions: os.system
os.spawn*
 Information about how the subprocess module can be used to replace these modules and functions can be found in the following sections.  See also PEP 324 – PEP proposing the subprocess module  Using the subprocess Module The recommended approach to invoking subprocesses is to use the run() function for all use cases it can handle. For more advanced use cases, the underlying Popen interface can be used directly. The run() function was added in Python 3.5; if you need to retain compatibility with older versions, see the Older high-level API section.
subprocess.run(args, *, stdin=None, input=None, stdout=None, stderr=None, capture_output=False, shell=False, cwd=None, timeout=None, check=False, encoding=None, errors=None, text=None, env=None, universal_newlines=None, **other_popen_kwargs)
Run the command described by args. Wait for command to complete, then return a CompletedProcess instance. The arguments shown above are merely the most common ones, described below in Frequently Used Arguments (hence the use of keyword-only notation in the abbreviated signature). The full function signature is largely the same as that of the Popen constructor - most of the arguments to this function are passed through to that interface. (timeout, input, check, and capture_output are not.) If capture_output is true, stdout and stderr will be captured. When used, the internal Popen object is automatically created with stdout=PIPE and stderr=PIPE. The stdout and stderr arguments may not be supplied at the same time as capture_output. If you wish to capture and combine both streams into one, use stdout=PIPE and stderr=STDOUT instead of capture_output. The timeout argument is passed to Popen.communicate(). If the timeout expires, the child process will be killed and waited for. The TimeoutExpired exception will be re-raised after the child process has terminated. The input argument is passed to Popen.communicate() and thus to the subprocess’s stdin. If used it must be a byte sequence, or a string if encoding or errors is specified or text is true. When used, the internal Popen object is automatically created with stdin=PIPE, and the stdin argument may not be used as well. If check is true, and the process exits with a non-zero exit code, a CalledProcessError exception will be raised. Attributes of that exception hold the arguments, the exit code, and stdout and stderr if they were captured. If encoding or errors are specified, or text is true, file objects for stdin, stdout and stderr are opened in text mode using the specified encoding and errors or the io.TextIOWrapper default. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode. If env is not None, it must be a mapping that defines the environment variables for the new process; these are used instead of the default behavior of inheriting the current process’ environment. It is passed directly to Popen. Examples: >>> subprocess.run(["ls", "-l"])  # doesn't capture output
CompletedProcess(args=['ls', '-l'], returncode=0)

>>> subprocess.run("exit 1", shell=True, check=True)
Traceback (most recent call last):
  ...
subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

>>> subprocess.run(["ls", "-l", "/dev/null"], capture_output=True)
CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n', stderr=b'')
  New in version 3.5.   Changed in version 3.6: Added encoding and errors parameters   Changed in version 3.7: Added the text parameter, as a more understandable alias of universal_newlines. Added the capture_output parameter.

class subprocess.CompletedProcess
The return value from run(), representing a process that has finished.
args
The arguments used to launch the process. This may be a list or a string.

returncode
Exit status of the child process. Typically, an exit status of 0 indicates that it ran successfully. A negative value -N indicates that the child was terminated by signal N (POSIX only).

stdout
Captured stdout from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stdout was not captured. If you ran the process with stderr=subprocess.STDOUT, stdout and stderr will be combined in this attribute, and stderr will be None.

stderr
Captured stderr from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stderr was not captured.

check_returncode()
If returncode is non-zero, raise a CalledProcessError.
  New in version 3.5.

subprocess.DEVNULL
Special value that can be used as the stdin, stdout or stderr argument to Popen and indicates that the special file os.devnull will be used.  New in version 3.3.

subprocess.PIPE
Special value that can be used as the stdin, stdout or stderr argument to Popen and indicates that a pipe to the standard stream should be opened. Most useful with Popen.communicate().

subprocess.STDOUT
Special value that can be used as the stderr argument to Popen and indicates that standard error should go into the same handle as standard output.

exception subprocess.SubprocessError
Base class for all other exceptions from this module.  New in version 3.3.

exception subprocess.TimeoutExpired
Subclass of SubprocessError, raised when a timeout expires while waiting for a child process.
cmd
Command that was used to spawn the child process.

timeout
Timeout in seconds.

output
Output of the child process if it was captured by run() or check_output(). Otherwise, None.

stdout
Alias for output, for symmetry with stderr.

stderr
Stderr output of the child process if it was captured by run(). Otherwise, None.
  New in version 3.3.   Changed in version 3.5: stdout and stderr attributes added

exception subprocess.CalledProcessError
Subclass of SubprocessError, raised when a process run by check_call() or check_output() returns a non-zero exit status.
returncode
Exit status of the child process. If the process exited due to a signal, this will be the negative signal number.

cmd
Command that was used to spawn the child process.

output
Output of the child process if it was captured by run() or check_output(). Otherwise, None.

stdout
Alias for output, for symmetry with stderr.

stderr
Stderr output of the child process if it was captured by run(). Otherwise, None.
  Changed in version 3.5: stdout and stderr attributes added
 Frequently Used Arguments To support a wide variety of use cases, the Popen constructor (and the convenience functions) accept a large number of optional arguments. For most typical use cases, many of these arguments can be safely left at their default values. The arguments that are most commonly needed are: args is required for all calls and should be a string, or a sequence of program arguments. Providing a sequence of arguments is generally preferred, as it allows the module to take care of any required escaping and quoting of arguments (e.g. to permit spaces in file names). If passing a single string, either shell must be True (see below) or else the string must simply name the program to be executed without specifying any arguments. stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. Valid values are PIPE, DEVNULL, an existing file descriptor (a positive integer), an existing file object, and None. PIPE indicates that a new pipe to the child should be created. DEVNULL indicates that the special file os.devnull will be used. With the default settings of None, no redirection will occur; the child’s file handles will be inherited from the parent. Additionally, stderr can be STDOUT, which indicates that the stderr data from the child process should be captured into the same file handle as for stdout. If encoding or errors are specified, or text (also known as universal_newlines) is true, the file objects stdin, stdout and stderr will be opened in text mode using the encoding and errors specified in the call or the defaults for io.TextIOWrapper. For stdin, line ending characters '\n' in the input will be converted to the default line separator os.linesep. For stdout and stderr, all line endings in the output will be converted to '\n'. For more information see the documentation of the io.TextIOWrapper class when the newline argument to its constructor is None. If text mode is not used, stdin, stdout and stderr will be opened as binary streams. No encoding or line ending conversion is performed.  New in version 3.6: Added encoding and errors parameters.   New in version 3.7: Added the text parameter as an alias for universal_newlines.   Note The newlines attribute of the file objects Popen.stdin, Popen.stdout and Popen.stderr are not updated by the Popen.communicate() method.  If shell is True, the specified command will be executed through the shell. This can be useful if you are using Python primarily for the enhanced control flow it offers over most system shells and still want convenient access to other shell features such as shell pipes, filename wildcards, environment variable expansion, and expansion of ~ to a user’s home directory. However, note that Python itself offers implementations of many shell-like features (in particular, glob, fnmatch, os.walk(), os.path.expandvars(), os.path.expanduser(), and shutil).  Changed in version 3.3: When universal_newlines is True, the class uses the encoding locale.getpreferredencoding(False) instead of locale.getpreferredencoding(). See the io.TextIOWrapper class for more information on this change.   Note Read the Security Considerations section before using shell=True.  These options, along with all of the other options, are described in more detail in the Popen constructor documentation. Popen Constructor The underlying process creation and management in this module is handled by the Popen class. It offers a lot of flexibility so that developers are able to handle the less common cases not covered by the convenience functions.
class subprocess.Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=True, shell=False, cwd=None, env=None, universal_newlines=None, startupinfo=None, creationflags=0, restore_signals=True, start_new_session=False, pass_fds=(), *, group=None, extra_groups=None, user=None, umask=-1, encoding=None, errors=None, text=None)
Execute a child program in a new process. On POSIX, the class uses os.execvp()-like behavior to execute the child program. On Windows, the class uses the Windows CreateProcess() function. The arguments to Popen are as follows. args should be a sequence of program arguments or else a single string or path-like object. By default, the program to execute is the first item in args if args is a sequence. If args is a string, the interpretation is platform-dependent and described below. See the shell and executable arguments for additional differences from the default behavior. Unless otherwise stated, it is recommended to pass args as a sequence. An example of passing some arguments to an external program as a sequence is: Popen(["/usr/bin/git", "commit", "-m", "Fixes a bug."])
 On POSIX, if args is a string, the string is interpreted as the name or path of the program to execute. However, this can only be done if not passing arguments to the program.  Note It may not be obvious how to break a shell command into a sequence of arguments, especially in complex cases. shlex.split() can illustrate how to determine the correct tokenization for args: >>> import shlex, subprocess
>>> command_line = input()
/bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'"
>>> args = shlex.split(command_line)
>>> print(args)
['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"]
>>> p = subprocess.Popen(args) # Success!
 Note in particular that options (such as -input) and arguments (such as eggs.txt) that are separated by whitespace in the shell go in separate list elements, while arguments that need quoting or backslash escaping when used in the shell (such as filenames containing spaces or the echo command shown above) are single list elements.  On Windows, if args is a sequence, it will be converted to a string in a manner described in Converting an argument sequence to a string on Windows. This is because the underlying CreateProcess() operates on strings.  Changed in version 3.6: args parameter accepts a path-like object if shell is False and a sequence containing path-like objects on POSIX.   Changed in version 3.8: args parameter accepts a path-like object if shell is False and a sequence containing bytes and path-like objects on Windows.  The shell argument (which defaults to False) specifies whether to use the shell as the program to execute. If shell is True, it is recommended to pass args as a string rather than as a sequence. On POSIX with shell=True, the shell defaults to /bin/sh. If args is a string, the string specifies the command to execute through the shell. This means that the string must be formatted exactly as it would be when typed at the shell prompt. This includes, for example, quoting or backslash escaping filenames with spaces in them. If args is a sequence, the first item specifies the command string, and any additional items will be treated as additional arguments to the shell itself. That is to say, Popen does the equivalent of: Popen(['/bin/sh', '-c', args[0], args[1], ...])
 On Windows with shell=True, the COMSPEC environment variable specifies the default shell. The only time you need to specify shell=True on Windows is when the command you wish to execute is built into the shell (e.g. dir or copy). You do not need shell=True to run a batch file or console-based executable.  Note Read the Security Considerations section before using shell=True.  bufsize will be supplied as the corresponding argument to the open() function when creating the stdin/stdout/stderr pipe file objects:
0 means unbuffered (read and write are one system call and can return short)
1 means line buffered (only usable if universal_newlines=True i.e., in a text mode) any other positive value means use a buffer of approximately that size negative bufsize (the default) means the system default of io.DEFAULT_BUFFER_SIZE will be used.   Changed in version 3.3.1: bufsize now defaults to -1 to enable buffering by default to match the behavior that most code expects. In versions prior to Python 3.2.4 and 3.3.1 it incorrectly defaulted to 0 which was unbuffered and allowed short reads. This was unintentional and did not match the behavior of Python 2 as most code expected.  The executable argument specifies a replacement program to execute. It is very seldom needed. When shell=False, executable replaces the program to execute specified by args. However, the original args is still passed to the program. Most programs treat the program specified by args as the command name, which can then be different from the program actually executed. On POSIX, the args name becomes the display name for the executable in utilities such as ps. If shell=True, on POSIX the executable argument specifies a replacement shell for the default /bin/sh.  Changed in version 3.6: executable parameter accepts a path-like object on POSIX.   Changed in version 3.8: executable parameter accepts a bytes and path-like object on Windows.  stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. Valid values are PIPE, DEVNULL, an existing file descriptor (a positive integer), an existing file object, and None. PIPE indicates that a new pipe to the child should be created. DEVNULL indicates that the special file os.devnull will be used. With the default settings of None, no redirection will occur; the child’s file handles will be inherited from the parent. Additionally, stderr can be STDOUT, which indicates that the stderr data from the applications should be captured into the same file handle as for stdout. If preexec_fn is set to a callable object, this object will be called in the child process just before the child is executed. (POSIX only)  Warning The preexec_fn parameter is not safe to use in the presence of threads in your application. The child process could deadlock before exec is called. If you must use it, keep it trivial! Minimize the number of libraries you call into.   Note If you need to modify the environment for the child use the env parameter rather than doing it in a preexec_fn. The start_new_session parameter can take the place of a previously common use of preexec_fn to call os.setsid() in the child.   Changed in version 3.8: The preexec_fn parameter is no longer supported in subinterpreters. The use of the parameter in a subinterpreter raises RuntimeError. The new restriction may affect applications that are deployed in mod_wsgi, uWSGI, and other embedded environments.  If close_fds is true, all file descriptors except 0, 1 and 2 will be closed before the child process is executed. Otherwise when close_fds is false, file descriptors obey their inheritable flag as described in Inheritance of File Descriptors. On Windows, if close_fds is true then no handles will be inherited by the child process unless explicitly passed in the handle_list element of STARTUPINFO.lpAttributeList, or by standard handle redirection.  Changed in version 3.2: The default for close_fds was changed from False to what is described above.   Changed in version 3.7: On Windows the default for close_fds was changed from False to True when redirecting the standard handles. It’s now possible to set close_fds to True when redirecting the standard handles.  pass_fds is an optional sequence of file descriptors to keep open between the parent and child. Providing any pass_fds forces close_fds to be True. (POSIX only)  Changed in version 3.2: The pass_fds parameter was added.  If cwd is not None, the function changes the working directory to cwd before executing the child. cwd can be a string, bytes or path-like object. In particular, the function looks for executable (or for the first item in args) relative to cwd if the executable path is a relative path.  Changed in version 3.6: cwd parameter accepts a path-like object on POSIX.   Changed in version 3.7: cwd parameter accepts a path-like object on Windows.   Changed in version 3.8: cwd parameter accepts a bytes object on Windows.  If restore_signals is true (the default) all signals that Python has set to SIG_IGN are restored to SIG_DFL in the child process before the exec. Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. (POSIX only)  Changed in version 3.2: restore_signals was added.  If start_new_session is true the setsid() system call will be made in the child process prior to the execution of the subprocess. (POSIX only)  Changed in version 3.2: start_new_session was added.  If group is not None, the setregid() system call will be made in the child process prior to the execution of the subprocess. If the provided value is a string, it will be looked up via grp.getgrnam() and the value in gr_gid will be used. If the value is an integer, it will be passed verbatim. (POSIX only) Availability: POSIX  New in version 3.9.  If extra_groups is not None, the setgroups() system call will be made in the child process prior to the execution of the subprocess. Strings provided in extra_groups will be looked up via grp.getgrnam() and the values in gr_gid will be used. Integer values will be passed verbatim. (POSIX only) Availability: POSIX  New in version 3.9.  If user is not None, the setreuid() system call will be made in the child process prior to the execution of the subprocess. If the provided value is a string, it will be looked up via pwd.getpwnam() and the value in pw_uid will be used. If the value is an integer, it will be passed verbatim. (POSIX only) Availability: POSIX  New in version 3.9.  If umask is not negative, the umask() system call will be made in the child process prior to the execution of the subprocess. Availability: POSIX  New in version 3.9.  If env is not None, it must be a mapping that defines the environment variables for the new process; these are used instead of the default behavior of inheriting the current process’ environment.  Note If specified, env must provide any variables required for the program to execute. On Windows, in order to run a side-by-side assembly the specified env must include a valid SystemRoot.  If encoding or errors are specified, or text is true, the file objects stdin, stdout and stderr are opened in text mode with the specified encoding and errors, as described above in Frequently Used Arguments. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode.  New in version 3.6: encoding and errors were added.   New in version 3.7: text was added as a more readable alias for universal_newlines.  If given, startupinfo will be a STARTUPINFO object, which is passed to the underlying CreateProcess function. creationflags, if given, can be one or more of the following flags:  CREATE_NEW_CONSOLE CREATE_NEW_PROCESS_GROUP ABOVE_NORMAL_PRIORITY_CLASS BELOW_NORMAL_PRIORITY_CLASS HIGH_PRIORITY_CLASS IDLE_PRIORITY_CLASS NORMAL_PRIORITY_CLASS REALTIME_PRIORITY_CLASS CREATE_NO_WINDOW DETACHED_PROCESS CREATE_DEFAULT_ERROR_MODE CREATE_BREAKAWAY_FROM_JOB  Popen objects are supported as context managers via the with statement: on exit, standard file descriptors are closed, and the process is waited for. with Popen(["ifconfig"], stdout=PIPE) as proc:
    log.write(proc.stdout.read())

Popen and the other functions in this module that use it raise an auditing event subprocess.Popen with arguments executable, args, cwd, and env. The value for args may be a single string or a list of strings, depending on platform.  Changed in version 3.2: Added context manager support.   Changed in version 3.6: Popen destructor now emits a ResourceWarning warning if the child process is still running.   Changed in version 3.8: Popen can use os.posix_spawn() in some cases for better performance. On Windows Subsystem for Linux and QEMU User Emulation, Popen constructor using os.posix_spawn() no longer raise an exception on errors like missing program, but the child process fails with a non-zero returncode.
 Exceptions Exceptions raised in the child process, before the new program has started to execute, will be re-raised in the parent. The most common exception raised is OSError. This occurs, for example, when trying to execute a non-existent file. Applications should prepare for OSError exceptions. A ValueError will be raised if Popen is called with invalid arguments. check_call() and check_output() will raise CalledProcessError if the called process returns a non-zero return code. All of the functions and methods that accept a timeout parameter, such as call() and Popen.communicate() will raise TimeoutExpired if the timeout expires before the process exits. Exceptions defined in this module all inherit from SubprocessError.  New in version 3.3: The SubprocessError base class was added.  Security Considerations Unlike some other popen functions, this implementation will never implicitly call a system shell. This means that all characters, including shell metacharacters, can safely be passed to child processes. If the shell is invoked explicitly, via shell=True, it is the application’s responsibility to ensure that all whitespace and metacharacters are quoted appropriately to avoid shell injection vulnerabilities. When using shell=True, the shlex.quote() function can be used to properly escape whitespace and shell metacharacters in strings that are going to be used to construct shell commands. Popen Objects Instances of the Popen class have the following methods:
Popen.poll()
Check if child process has terminated. Set and return returncode attribute. Otherwise, returns None.

Popen.wait(timeout=None)
Wait for child process to terminate. Set and return returncode attribute. If the process does not terminate after timeout seconds, raise a TimeoutExpired exception. It is safe to catch this exception and retry the wait.  Note This will deadlock when using stdout=PIPE or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use Popen.communicate() when using pipes to avoid that.   Note The function is implemented using a busy loop (non-blocking call and short sleeps). Use the asyncio module for an asynchronous wait: see asyncio.create_subprocess_exec.   Changed in version 3.3: timeout was added.

Popen.communicate(input=None, timeout=None)
Interact with process: Send data to stdin. Read data from stdout and stderr, until end-of-file is reached. Wait for process to terminate and set the returncode attribute. The optional input argument should be data to be sent to the child process, or None, if no data should be sent to the child. If streams were opened in text mode, input must be a string. Otherwise, it must be bytes. communicate() returns a tuple (stdout_data, stderr_data). The data will be strings if streams were opened in text mode; otherwise, bytes. Note that if you want to send data to the process’s stdin, you need to create the Popen object with stdin=PIPE. Similarly, to get anything other than None in the result tuple, you need to give stdout=PIPE and/or stderr=PIPE too. If the process does not terminate after timeout seconds, a TimeoutExpired exception will be raised. Catching this exception and retrying communication will not lose any output. The child process is not killed if the timeout expires, so in order to cleanup properly a well-behaved application should kill the child process and finish communication: proc = subprocess.Popen(...)
try:
    outs, errs = proc.communicate(timeout=15)
except TimeoutExpired:
    proc.kill()
    outs, errs = proc.communicate()
  Note The data read is buffered in memory, so do not use this method if the data size is large or unlimited.   Changed in version 3.3: timeout was added.

Popen.send_signal(signal)
Sends the signal signal to the child. Do nothing if the process completed.  Note On Windows, SIGTERM is an alias for terminate(). CTRL_C_EVENT and CTRL_BREAK_EVENT can be sent to processes started with a creationflags parameter which includes CREATE_NEW_PROCESS_GROUP.

Popen.terminate()
Stop the child. On POSIX OSs the method sends SIGTERM to the child. On Windows the Win32 API function TerminateProcess() is called to stop the child.

Popen.kill()
Kills the child. On POSIX OSs the function sends SIGKILL to the child. On Windows kill() is an alias for terminate().
 The following attributes are also available:
Popen.args
The args argument as it was passed to Popen – a sequence of program arguments or else a single string.  New in version 3.3.

Popen.stdin
If the stdin argument was PIPE, this attribute is a writeable stream object as returned by open(). If the encoding or errors arguments were specified or the universal_newlines argument was True, the stream is a text stream, otherwise it is a byte stream. If the stdin argument was not PIPE, this attribute is None.

Popen.stdout
If the stdout argument was PIPE, this attribute is a readable stream object as returned by open(). Reading from the stream provides output from the child process. If the encoding or errors arguments were specified or the universal_newlines argument was True, the stream is a text stream, otherwise it is a byte stream. If the stdout argument was not PIPE, this attribute is None.

Popen.stderr
If the stderr argument was PIPE, this attribute is a readable stream object as returned by open(). Reading from the stream provides error output from the child process. If the encoding or errors arguments were specified or the universal_newlines argument was True, the stream is a text stream, otherwise it is a byte stream. If the stderr argument was not PIPE, this attribute is None.
  Warning Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS pipe buffers filling up and blocking the child process.
Popen.pid
The process ID of the child process. Note that if you set the shell argument to True, this is the process ID of the spawned shell.

Popen.returncode
The child return code, set by poll() and wait() (and indirectly by communicate()). A None value indicates that the process hasn’t terminated yet. A negative value -N indicates that the child was terminated by signal N (POSIX only).
 Windows Popen Helpers The STARTUPINFO class and following constants are only available on Windows.
class subprocess.STARTUPINFO(*, dwFlags=0, hStdInput=None, hStdOutput=None, hStdError=None, wShowWindow=0, lpAttributeList=None)
Partial support of the Windows STARTUPINFO structure is used for Popen creation. The following attributes can be set by passing them as keyword-only arguments.  Changed in version 3.7: Keyword-only argument support was added.
dwFlags
A bit field that determines whether certain STARTUPINFO attributes are used when the process creates a window. si = subprocess.STARTUPINFO()
si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW

hStdInput
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard input handle for the process. If STARTF_USESTDHANDLES is not specified, the default for standard input is the keyboard buffer.

hStdOutput
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard output handle for the process. Otherwise, this attribute is ignored and the default for standard output is the console window’s buffer.

hStdError
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard error handle for the process. Otherwise, this attribute is ignored and the default for standard error is the console window’s buffer.

wShowWindow
If dwFlags specifies STARTF_USESHOWWINDOW, this attribute can be any of the values that can be specified in the nCmdShow parameter for the ShowWindow function, except for SW_SHOWDEFAULT. Otherwise, this attribute is ignored. SW_HIDE is provided for this attribute. It is used when Popen is called with shell=True.

lpAttributeList
A dictionary of additional attributes for process creation as given in STARTUPINFOEX, see UpdateProcThreadAttribute. Supported attributes:  handle_list

Sequence of handles that will be inherited. close_fds must be true if non-empty. The handles must be temporarily made inheritable by os.set_handle_inheritable() when passed to the Popen constructor, else OSError will be raised with Windows error ERROR_INVALID_PARAMETER (87).  Warning In a multithreaded process, use caution to avoid leaking handles that are marked inheritable when combining this feature with concurrent calls to other process creation functions that inherit all handles such as os.system(). This also applies to standard handle redirection, which temporarily creates inheritable handles.     New in version 3.7.

 Windows Constants The subprocess module exposes the following constants.
subprocess.STD_INPUT_HANDLE
The standard input device. Initially, this is the console input buffer, CONIN$.

subprocess.STD_OUTPUT_HANDLE
The standard output device. Initially, this is the active console screen buffer, CONOUT$.

subprocess.STD_ERROR_HANDLE
The standard error device. Initially, this is the active console screen buffer, CONOUT$.

subprocess.SW_HIDE
Hides the window. Another window will be activated.

subprocess.STARTF_USESTDHANDLES
Specifies that the STARTUPINFO.hStdInput, STARTUPINFO.hStdOutput, and STARTUPINFO.hStdError attributes contain additional information.

subprocess.STARTF_USESHOWWINDOW
Specifies that the STARTUPINFO.wShowWindow attribute contains additional information.

subprocess.CREATE_NEW_CONSOLE
The new process has a new console, instead of inheriting its parent’s console (the default).

subprocess.CREATE_NEW_PROCESS_GROUP
A Popen creationflags parameter to specify that a new process group will be created. This flag is necessary for using os.kill() on the subprocess. This flag is ignored if CREATE_NEW_CONSOLE is specified.

subprocess.ABOVE_NORMAL_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have an above average priority.  New in version 3.7.

subprocess.BELOW_NORMAL_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have a below average priority.  New in version 3.7.

subprocess.HIGH_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have a high priority.  New in version 3.7.

subprocess.IDLE_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have an idle (lowest) priority.  New in version 3.7.

subprocess.NORMAL_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have an normal priority. (default)  New in version 3.7.

subprocess.REALTIME_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have realtime priority. You should almost never use REALTIME_PRIORITY_CLASS, because this interrupts system threads that manage mouse input, keyboard input, and background disk flushing. This class can be appropriate for applications that “talk” directly to hardware or that perform brief tasks that should have limited interruptions.  New in version 3.7.

subprocess.CREATE_NO_WINDOW
A Popen creationflags parameter to specify that a new process will not create a window.  New in version 3.7.

subprocess.DETACHED_PROCESS
A Popen creationflags parameter to specify that a new process will not inherit its parent’s console. This value cannot be used with CREATE_NEW_CONSOLE.  New in version 3.7.

subprocess.CREATE_DEFAULT_ERROR_MODE
A Popen creationflags parameter to specify that a new process does not inherit the error mode of the calling process. Instead, the new process gets the default error mode. This feature is particularly useful for multithreaded shell applications that run with hard errors disabled.  New in version 3.7.

subprocess.CREATE_BREAKAWAY_FROM_JOB
A Popen creationflags parameter to specify that a new process is not associated with the job.  New in version 3.7.
 Older high-level API Prior to Python 3.5, these three functions comprised the high level API to subprocess. You can now use run() in many cases, but lots of existing code calls these functions.
subprocess.call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, **other_popen_kwargs)
Run the command described by args. Wait for command to complete, then return the returncode attribute. Code needing to capture stdout or stderr should use run() instead: run(...).returncode
 To suppress stdout or stderr, supply a value of DEVNULL. The arguments shown above are merely some common ones. The full function signature is the same as that of the Popen constructor - this function passes all supplied arguments other than timeout directly through to that interface.  Note Do not use stdout=PIPE or stderr=PIPE with this function. The child process will block if it generates enough output to a pipe to fill up the OS pipe buffer as the pipes are not being read from.   Changed in version 3.3: timeout was added.

subprocess.check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, **other_popen_kwargs)
Run command with arguments. Wait for command to complete. If the return code was zero then return, otherwise raise CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute. Code needing to capture stdout or stderr should use run() instead: run(..., check=True)
 To suppress stdout or stderr, supply a value of DEVNULL. The arguments shown above are merely some common ones. The full function signature is the same as that of the Popen constructor - this function passes all supplied arguments other than timeout directly through to that interface.  Note Do not use stdout=PIPE or stderr=PIPE with this function. The child process will block if it generates enough output to a pipe to fill up the OS pipe buffer as the pipes are not being read from.   Changed in version 3.3: timeout was added.

subprocess.check_output(args, *, stdin=None, stderr=None, shell=False, cwd=None, encoding=None, errors=None, universal_newlines=None, timeout=None, text=None, **other_popen_kwargs)
Run command with arguments and return its output. If the return code was non-zero it raises a CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute and any output in the output attribute. This is equivalent to: run(..., check=True, stdout=PIPE).stdout
 The arguments shown above are merely some common ones. The full function signature is largely the same as that of run() - most arguments are passed directly through to that interface. One API deviation from run() behavior exists: passing input=None will behave the same as input=b'' (or input='', depending on other arguments) rather than using the parent’s standard input file handle. By default, this function will return the data as encoded bytes. The actual encoding of the output data may depend on the command being invoked, so the decoding to text will often need to be handled at the application level. This behaviour may be overridden by setting text, encoding, errors, or universal_newlines to True as described in Frequently Used Arguments and run(). To also capture standard error in the result, use stderr=subprocess.STDOUT: >>> subprocess.check_output(
...     "ls non_existent_file; exit 0",
...     stderr=subprocess.STDOUT,
...     shell=True)
'ls: non_existent_file: No such file or directory\n'
  New in version 3.1.   Changed in version 3.3: timeout was added.   Changed in version 3.4: Support for the input keyword argument was added.   Changed in version 3.6: encoding and errors were added. See run() for details.   New in version 3.7: text was added as a more readable alias for universal_newlines.
 Replacing Older Functions with the subprocess Module In this section, “a becomes b” means that b can be used as a replacement for a.  Note All “a” functions in this section fail (more or less) silently if the executed program cannot be found; the “b” replacements raise OSError instead. In addition, the replacements using check_output() will fail with a CalledProcessError if the requested operation produces a non-zero return code. The output is still available as the output attribute of the raised exception.  In the following examples, we assume that the relevant functions have already been imported from the subprocess module. Replacing /bin/sh shell command substitution output=$(mycmd myarg)
 becomes: output = check_output(["mycmd", "myarg"])
 Replacing shell pipeline output=$(dmesg | grep hda)
 becomes: p1 = Popen(["dmesg"], stdout=PIPE)
p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
output = p2.communicate()[0]
 The p1.stdout.close() call after starting the p2 is important in order for p1 to receive a SIGPIPE if p2 exits before p1. Alternatively, for trusted input, the shell’s own pipeline support may still be used directly: output=$(dmesg | grep hda)
 becomes: output=check_output("dmesg | grep hda", shell=True)
 Replacing os.system()
 sts = os.system("mycmd" + " myarg")
# becomes
sts = call("mycmd" + " myarg", shell=True)
 Notes:  Calling the program through the shell is usually not required.  A more realistic example would look like this: try:
    retcode = call("mycmd" + " myarg", shell=True)
    if retcode < 0:
        print("Child was terminated by signal", -retcode, file=sys.stderr)
    else:
        print("Child returned", retcode, file=sys.stderr)
except OSError as e:
    print("Execution failed:", e, file=sys.stderr)
 Replacing the os.spawn family P_NOWAIT example: pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg")
==>
pid = Popen(["/bin/mycmd", "myarg"]).pid
 P_WAIT example: retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg")
==>
retcode = call(["/bin/mycmd", "myarg"])
 Vector example: os.spawnvp(os.P_NOWAIT, path, args)
==>
Popen([path] + args[1:])
 Environment example: os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env)
==>
Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"})
 Replacing os.popen(), os.popen2(), os.popen3()
 (child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize)
==>
p = Popen(cmd, shell=True, bufsize=bufsize,
          stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdin, child_stdout) = (p.stdin, p.stdout)
 (child_stdin,
 child_stdout,
 child_stderr) = os.popen3(cmd, mode, bufsize)
==>
p = Popen(cmd, shell=True, bufsize=bufsize,
          stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)
(child_stdin,
 child_stdout,
 child_stderr) = (p.stdin, p.stdout, p.stderr)
 (child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize)
==>
p = Popen(cmd, shell=True, bufsize=bufsize,
          stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
(child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout)
 Return code handling translates as follows: pipe = os.popen(cmd, 'w')
...
rc = pipe.close()
if rc is not None and rc >> 8:
    print("There were some errors")
==>
process = Popen(cmd, stdin=PIPE)
...
process.stdin.close()
if process.wait() != 0:
    print("There were some errors")
 Replacing functions from the popen2 module  Note If the cmd argument to popen2 functions is a string, the command is executed through /bin/sh. If it is a list, the command is directly executed.  (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode)
==>
p = Popen("somestring", shell=True, bufsize=bufsize,
          stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdout, child_stdin) = (p.stdout, p.stdin)
 (child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, mode)
==>
p = Popen(["mycmd", "myarg"], bufsize=bufsize,
          stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdout, child_stdin) = (p.stdout, p.stdin)
 popen2.Popen3 and popen2.Popen4 basically work as subprocess.Popen, except that:
Popen raises an exception if the execution fails. The capturestderr argument is replaced with the stderr argument.
stdin=PIPE and stdout=PIPE must be specified. popen2 closes all file descriptors by default, but you have to specify close_fds=True with Popen to guarantee this behavior on all platforms or past Python versions.  Legacy Shell Invocation Functions This module also provides the following legacy functions from the 2.x commands module. These operations implicitly invoke the system shell and none of the guarantees described above regarding security and exception handling consistency are valid for these functions.
subprocess.getstatusoutput(cmd)
Return (exitcode, output) of executing cmd in a shell. Execute the string cmd in a shell with Popen.check_output() and return a 2-tuple (exitcode, output). The locale encoding is used; see the notes on Frequently Used Arguments for more details. A trailing newline is stripped from the output. The exit code for the command can be interpreted as the return code of subprocess. Example: >>> subprocess.getstatusoutput('ls /bin/ls')
(0, '/bin/ls')
>>> subprocess.getstatusoutput('cat /bin/junk')
(1, 'cat: /bin/junk: No such file or directory')
>>> subprocess.getstatusoutput('/bin/junk')
(127, 'sh: /bin/junk: not found')
>>> subprocess.getstatusoutput('/bin/kill $$')
(-15, '')
 Availability: POSIX & Windows.  Changed in version 3.3.4: Windows support was added. The function now returns (exitcode, output) instead of (status, output) as it did in Python 3.3.3 and earlier. exitcode has the same value as returncode.

subprocess.getoutput(cmd)
Return output (stdout and stderr) of executing cmd in a shell. Like getstatusoutput(), except the exit code is ignored and the return value is a string containing the command’s output. Example: >>> subprocess.getoutput('ls /bin/ls')
'/bin/ls'
 Availability: POSIX & Windows.  Changed in version 3.3.4: Windows support added
 Notes Converting an argument sequence to a string on Windows On Windows, an args sequence is converted to a string that can be parsed using the following rules (which correspond to the rules used by the MS C runtime):  Arguments are delimited by white space, which is either a space or a tab. A string surrounded by double quotation marks is interpreted as a single argument, regardless of white space contained within. A quoted string can be embedded in an argument. A double quotation mark preceded by a backslash is interpreted as a literal double quotation mark. Backslashes are interpreted literally, unless they immediately precede a double quotation mark. If backslashes immediately precede a double quotation mark, every pair of backslashes is interpreted as a literal backslash. If the number of backslashes is odd, the last backslash escapes the next double quotation mark as described in rule 3.   See also
shlex

Module which provides function to parse and escape command lines.


subprocess.ABOVE_NORMAL_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have an above average priority.  New in version 3.7.


subprocess.BELOW_NORMAL_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have a below average priority.  New in version 3.7.


subprocess.call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, **other_popen_kwargs)
Run the command described by args. Wait for command to complete, then return the returncode attribute. Code needing to capture stdout or stderr should use run() instead: run(...).returncode
 To suppress stdout or stderr, supply a value of DEVNULL. The arguments shown above are merely some common ones. The full function signature is the same as that of the Popen constructor - this function passes all supplied arguments other than timeout directly through to that interface.  Note Do not use stdout=PIPE or stderr=PIPE with this function. The child process will block if it generates enough output to a pipe to fill up the OS pipe buffer as the pipes are not being read from.   Changed in version 3.3: timeout was added.


exception subprocess.CalledProcessError
Subclass of SubprocessError, raised when a process run by check_call() or check_output() returns a non-zero exit status.
returncode
Exit status of the child process. If the process exited due to a signal, this will be the negative signal number.

cmd
Command that was used to spawn the child process.

output
Output of the child process if it was captured by run() or check_output(). Otherwise, None.

stdout
Alias for output, for symmetry with stderr.

stderr
Stderr output of the child process if it was captured by run(). Otherwise, None.
  Changed in version 3.5: stdout and stderr attributes added


cmd
Command that was used to spawn the child process.


output
Output of the child process if it was captured by run() or check_output(). Otherwise, None.


returncode
Exit status of the child process. If the process exited due to a signal, this will be the negative signal number.


stderr
Stderr output of the child process if it was captured by run(). Otherwise, None.


stdout
Alias for output, for symmetry with stderr.


subprocess.check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False, cwd=None, timeout=None, **other_popen_kwargs)
Run command with arguments. Wait for command to complete. If the return code was zero then return, otherwise raise CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute. Code needing to capture stdout or stderr should use run() instead: run(..., check=True)
 To suppress stdout or stderr, supply a value of DEVNULL. The arguments shown above are merely some common ones. The full function signature is the same as that of the Popen constructor - this function passes all supplied arguments other than timeout directly through to that interface.  Note Do not use stdout=PIPE or stderr=PIPE with this function. The child process will block if it generates enough output to a pipe to fill up the OS pipe buffer as the pipes are not being read from.   Changed in version 3.3: timeout was added.


subprocess.check_output(args, *, stdin=None, stderr=None, shell=False, cwd=None, encoding=None, errors=None, universal_newlines=None, timeout=None, text=None, **other_popen_kwargs)
Run command with arguments and return its output. If the return code was non-zero it raises a CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute and any output in the output attribute. This is equivalent to: run(..., check=True, stdout=PIPE).stdout
 The arguments shown above are merely some common ones. The full function signature is largely the same as that of run() - most arguments are passed directly through to that interface. One API deviation from run() behavior exists: passing input=None will behave the same as input=b'' (or input='', depending on other arguments) rather than using the parent’s standard input file handle. By default, this function will return the data as encoded bytes. The actual encoding of the output data may depend on the command being invoked, so the decoding to text will often need to be handled at the application level. This behaviour may be overridden by setting text, encoding, errors, or universal_newlines to True as described in Frequently Used Arguments and run(). To also capture standard error in the result, use stderr=subprocess.STDOUT: >>> subprocess.check_output(
...     "ls non_existent_file; exit 0",
...     stderr=subprocess.STDOUT,
...     shell=True)
'ls: non_existent_file: No such file or directory\n'
  New in version 3.1.   Changed in version 3.3: timeout was added.   Changed in version 3.4: Support for the input keyword argument was added.   Changed in version 3.6: encoding and errors were added. See run() for details.   New in version 3.7: text was added as a more readable alias for universal_newlines.


class subprocess.CompletedProcess
The return value from run(), representing a process that has finished.
args
The arguments used to launch the process. This may be a list or a string.

returncode
Exit status of the child process. Typically, an exit status of 0 indicates that it ran successfully. A negative value -N indicates that the child was terminated by signal N (POSIX only).

stdout
Captured stdout from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stdout was not captured. If you ran the process with stderr=subprocess.STDOUT, stdout and stderr will be combined in this attribute, and stderr will be None.

stderr
Captured stderr from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stderr was not captured.

check_returncode()
If returncode is non-zero, raise a CalledProcessError.
  New in version 3.5.


args
The arguments used to launch the process. This may be a list or a string.


check_returncode()
If returncode is non-zero, raise a CalledProcessError.


returncode
Exit status of the child process. Typically, an exit status of 0 indicates that it ran successfully. A negative value -N indicates that the child was terminated by signal N (POSIX only).


stderr
Captured stderr from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stderr was not captured.


stdout
Captured stdout from the child process. A bytes sequence, or a string if run() was called with an encoding, errors, or text=True. None if stdout was not captured. If you ran the process with stderr=subprocess.STDOUT, stdout and stderr will be combined in this attribute, and stderr will be None.


subprocess.CREATE_BREAKAWAY_FROM_JOB
A Popen creationflags parameter to specify that a new process is not associated with the job.  New in version 3.7.


subprocess.CREATE_DEFAULT_ERROR_MODE
A Popen creationflags parameter to specify that a new process does not inherit the error mode of the calling process. Instead, the new process gets the default error mode. This feature is particularly useful for multithreaded shell applications that run with hard errors disabled.  New in version 3.7.


subprocess.CREATE_NEW_CONSOLE
The new process has a new console, instead of inheriting its parent’s console (the default).


subprocess.CREATE_NEW_PROCESS_GROUP
A Popen creationflags parameter to specify that a new process group will be created. This flag is necessary for using os.kill() on the subprocess. This flag is ignored if CREATE_NEW_CONSOLE is specified.


subprocess.CREATE_NO_WINDOW
A Popen creationflags parameter to specify that a new process will not create a window.  New in version 3.7.


subprocess.DETACHED_PROCESS
A Popen creationflags parameter to specify that a new process will not inherit its parent’s console. This value cannot be used with CREATE_NEW_CONSOLE.  New in version 3.7.


subprocess.DEVNULL
Special value that can be used as the stdin, stdout or stderr argument to Popen and indicates that the special file os.devnull will be used.  New in version 3.3.


subprocess.getoutput(cmd)
Return output (stdout and stderr) of executing cmd in a shell. Like getstatusoutput(), except the exit code is ignored and the return value is a string containing the command’s output. Example: >>> subprocess.getoutput('ls /bin/ls')
'/bin/ls'
 Availability: POSIX & Windows.  Changed in version 3.3.4: Windows support added


subprocess.getstatusoutput(cmd)
Return (exitcode, output) of executing cmd in a shell. Execute the string cmd in a shell with Popen.check_output() and return a 2-tuple (exitcode, output). The locale encoding is used; see the notes on Frequently Used Arguments for more details. A trailing newline is stripped from the output. The exit code for the command can be interpreted as the return code of subprocess. Example: >>> subprocess.getstatusoutput('ls /bin/ls')
(0, '/bin/ls')
>>> subprocess.getstatusoutput('cat /bin/junk')
(1, 'cat: /bin/junk: No such file or directory')
>>> subprocess.getstatusoutput('/bin/junk')
(127, 'sh: /bin/junk: not found')
>>> subprocess.getstatusoutput('/bin/kill $$')
(-15, '')
 Availability: POSIX & Windows.  Changed in version 3.3.4: Windows support was added. The function now returns (exitcode, output) instead of (status, output) as it did in Python 3.3.3 and earlier. exitcode has the same value as returncode.


subprocess.HIGH_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have a high priority.  New in version 3.7.


subprocess.IDLE_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have an idle (lowest) priority.  New in version 3.7.


subprocess.NORMAL_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have an normal priority. (default)  New in version 3.7.


subprocess.PIPE
Special value that can be used as the stdin, stdout or stderr argument to Popen and indicates that a pipe to the standard stream should be opened. Most useful with Popen.communicate().


class subprocess.Popen(args, bufsize=-1, executable=None, stdin=None, stdout=None, stderr=None, preexec_fn=None, close_fds=True, shell=False, cwd=None, env=None, universal_newlines=None, startupinfo=None, creationflags=0, restore_signals=True, start_new_session=False, pass_fds=(), *, group=None, extra_groups=None, user=None, umask=-1, encoding=None, errors=None, text=None)
Execute a child program in a new process. On POSIX, the class uses os.execvp()-like behavior to execute the child program. On Windows, the class uses the Windows CreateProcess() function. The arguments to Popen are as follows. args should be a sequence of program arguments or else a single string or path-like object. By default, the program to execute is the first item in args if args is a sequence. If args is a string, the interpretation is platform-dependent and described below. See the shell and executable arguments for additional differences from the default behavior. Unless otherwise stated, it is recommended to pass args as a sequence. An example of passing some arguments to an external program as a sequence is: Popen(["/usr/bin/git", "commit", "-m", "Fixes a bug."])
 On POSIX, if args is a string, the string is interpreted as the name or path of the program to execute. However, this can only be done if not passing arguments to the program.  Note It may not be obvious how to break a shell command into a sequence of arguments, especially in complex cases. shlex.split() can illustrate how to determine the correct tokenization for args: >>> import shlex, subprocess
>>> command_line = input()
/bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'"
>>> args = shlex.split(command_line)
>>> print(args)
['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"]
>>> p = subprocess.Popen(args) # Success!
 Note in particular that options (such as -input) and arguments (such as eggs.txt) that are separated by whitespace in the shell go in separate list elements, while arguments that need quoting or backslash escaping when used in the shell (such as filenames containing spaces or the echo command shown above) are single list elements.  On Windows, if args is a sequence, it will be converted to a string in a manner described in Converting an argument sequence to a string on Windows. This is because the underlying CreateProcess() operates on strings.  Changed in version 3.6: args parameter accepts a path-like object if shell is False and a sequence containing path-like objects on POSIX.   Changed in version 3.8: args parameter accepts a path-like object if shell is False and a sequence containing bytes and path-like objects on Windows.  The shell argument (which defaults to False) specifies whether to use the shell as the program to execute. If shell is True, it is recommended to pass args as a string rather than as a sequence. On POSIX with shell=True, the shell defaults to /bin/sh. If args is a string, the string specifies the command to execute through the shell. This means that the string must be formatted exactly as it would be when typed at the shell prompt. This includes, for example, quoting or backslash escaping filenames with spaces in them. If args is a sequence, the first item specifies the command string, and any additional items will be treated as additional arguments to the shell itself. That is to say, Popen does the equivalent of: Popen(['/bin/sh', '-c', args[0], args[1], ...])
 On Windows with shell=True, the COMSPEC environment variable specifies the default shell. The only time you need to specify shell=True on Windows is when the command you wish to execute is built into the shell (e.g. dir or copy). You do not need shell=True to run a batch file or console-based executable.  Note Read the Security Considerations section before using shell=True.  bufsize will be supplied as the corresponding argument to the open() function when creating the stdin/stdout/stderr pipe file objects:
0 means unbuffered (read and write are one system call and can return short)
1 means line buffered (only usable if universal_newlines=True i.e., in a text mode) any other positive value means use a buffer of approximately that size negative bufsize (the default) means the system default of io.DEFAULT_BUFFER_SIZE will be used.   Changed in version 3.3.1: bufsize now defaults to -1 to enable buffering by default to match the behavior that most code expects. In versions prior to Python 3.2.4 and 3.3.1 it incorrectly defaulted to 0 which was unbuffered and allowed short reads. This was unintentional and did not match the behavior of Python 2 as most code expected.  The executable argument specifies a replacement program to execute. It is very seldom needed. When shell=False, executable replaces the program to execute specified by args. However, the original args is still passed to the program. Most programs treat the program specified by args as the command name, which can then be different from the program actually executed. On POSIX, the args name becomes the display name for the executable in utilities such as ps. If shell=True, on POSIX the executable argument specifies a replacement shell for the default /bin/sh.  Changed in version 3.6: executable parameter accepts a path-like object on POSIX.   Changed in version 3.8: executable parameter accepts a bytes and path-like object on Windows.  stdin, stdout and stderr specify the executed program’s standard input, standard output and standard error file handles, respectively. Valid values are PIPE, DEVNULL, an existing file descriptor (a positive integer), an existing file object, and None. PIPE indicates that a new pipe to the child should be created. DEVNULL indicates that the special file os.devnull will be used. With the default settings of None, no redirection will occur; the child’s file handles will be inherited from the parent. Additionally, stderr can be STDOUT, which indicates that the stderr data from the applications should be captured into the same file handle as for stdout. If preexec_fn is set to a callable object, this object will be called in the child process just before the child is executed. (POSIX only)  Warning The preexec_fn parameter is not safe to use in the presence of threads in your application. The child process could deadlock before exec is called. If you must use it, keep it trivial! Minimize the number of libraries you call into.   Note If you need to modify the environment for the child use the env parameter rather than doing it in a preexec_fn. The start_new_session parameter can take the place of a previously common use of preexec_fn to call os.setsid() in the child.   Changed in version 3.8: The preexec_fn parameter is no longer supported in subinterpreters. The use of the parameter in a subinterpreter raises RuntimeError. The new restriction may affect applications that are deployed in mod_wsgi, uWSGI, and other embedded environments.  If close_fds is true, all file descriptors except 0, 1 and 2 will be closed before the child process is executed. Otherwise when close_fds is false, file descriptors obey their inheritable flag as described in Inheritance of File Descriptors. On Windows, if close_fds is true then no handles will be inherited by the child process unless explicitly passed in the handle_list element of STARTUPINFO.lpAttributeList, or by standard handle redirection.  Changed in version 3.2: The default for close_fds was changed from False to what is described above.   Changed in version 3.7: On Windows the default for close_fds was changed from False to True when redirecting the standard handles. It’s now possible to set close_fds to True when redirecting the standard handles.  pass_fds is an optional sequence of file descriptors to keep open between the parent and child. Providing any pass_fds forces close_fds to be True. (POSIX only)  Changed in version 3.2: The pass_fds parameter was added.  If cwd is not None, the function changes the working directory to cwd before executing the child. cwd can be a string, bytes or path-like object. In particular, the function looks for executable (or for the first item in args) relative to cwd if the executable path is a relative path.  Changed in version 3.6: cwd parameter accepts a path-like object on POSIX.   Changed in version 3.7: cwd parameter accepts a path-like object on Windows.   Changed in version 3.8: cwd parameter accepts a bytes object on Windows.  If restore_signals is true (the default) all signals that Python has set to SIG_IGN are restored to SIG_DFL in the child process before the exec. Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals. (POSIX only)  Changed in version 3.2: restore_signals was added.  If start_new_session is true the setsid() system call will be made in the child process prior to the execution of the subprocess. (POSIX only)  Changed in version 3.2: start_new_session was added.  If group is not None, the setregid() system call will be made in the child process prior to the execution of the subprocess. If the provided value is a string, it will be looked up via grp.getgrnam() and the value in gr_gid will be used. If the value is an integer, it will be passed verbatim. (POSIX only) Availability: POSIX  New in version 3.9.  If extra_groups is not None, the setgroups() system call will be made in the child process prior to the execution of the subprocess. Strings provided in extra_groups will be looked up via grp.getgrnam() and the values in gr_gid will be used. Integer values will be passed verbatim. (POSIX only) Availability: POSIX  New in version 3.9.  If user is not None, the setreuid() system call will be made in the child process prior to the execution of the subprocess. If the provided value is a string, it will be looked up via pwd.getpwnam() and the value in pw_uid will be used. If the value is an integer, it will be passed verbatim. (POSIX only) Availability: POSIX  New in version 3.9.  If umask is not negative, the umask() system call will be made in the child process prior to the execution of the subprocess. Availability: POSIX  New in version 3.9.  If env is not None, it must be a mapping that defines the environment variables for the new process; these are used instead of the default behavior of inheriting the current process’ environment.  Note If specified, env must provide any variables required for the program to execute. On Windows, in order to run a side-by-side assembly the specified env must include a valid SystemRoot.  If encoding or errors are specified, or text is true, the file objects stdin, stdout and stderr are opened in text mode with the specified encoding and errors, as described above in Frequently Used Arguments. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode.  New in version 3.6: encoding and errors were added.   New in version 3.7: text was added as a more readable alias for universal_newlines.  If given, startupinfo will be a STARTUPINFO object, which is passed to the underlying CreateProcess function. creationflags, if given, can be one or more of the following flags:  CREATE_NEW_CONSOLE CREATE_NEW_PROCESS_GROUP ABOVE_NORMAL_PRIORITY_CLASS BELOW_NORMAL_PRIORITY_CLASS HIGH_PRIORITY_CLASS IDLE_PRIORITY_CLASS NORMAL_PRIORITY_CLASS REALTIME_PRIORITY_CLASS CREATE_NO_WINDOW DETACHED_PROCESS CREATE_DEFAULT_ERROR_MODE CREATE_BREAKAWAY_FROM_JOB  Popen objects are supported as context managers via the with statement: on exit, standard file descriptors are closed, and the process is waited for. with Popen(["ifconfig"], stdout=PIPE) as proc:
    log.write(proc.stdout.read())

Popen and the other functions in this module that use it raise an auditing event subprocess.Popen with arguments executable, args, cwd, and env. The value for args may be a single string or a list of strings, depending on platform.  Changed in version 3.2: Added context manager support.   Changed in version 3.6: Popen destructor now emits a ResourceWarning warning if the child process is still running.   Changed in version 3.8: Popen can use os.posix_spawn() in some cases for better performance. On Windows Subsystem for Linux and QEMU User Emulation, Popen constructor using os.posix_spawn() no longer raise an exception on errors like missing program, but the child process fails with a non-zero returncode.


Popen.args
The args argument as it was passed to Popen – a sequence of program arguments or else a single string.  New in version 3.3.


Popen.communicate(input=None, timeout=None)
Interact with process: Send data to stdin. Read data from stdout and stderr, until end-of-file is reached. Wait for process to terminate and set the returncode attribute. The optional input argument should be data to be sent to the child process, or None, if no data should be sent to the child. If streams were opened in text mode, input must be a string. Otherwise, it must be bytes. communicate() returns a tuple (stdout_data, stderr_data). The data will be strings if streams were opened in text mode; otherwise, bytes. Note that if you want to send data to the process’s stdin, you need to create the Popen object with stdin=PIPE. Similarly, to get anything other than None in the result tuple, you need to give stdout=PIPE and/or stderr=PIPE too. If the process does not terminate after timeout seconds, a TimeoutExpired exception will be raised. Catching this exception and retrying communication will not lose any output. The child process is not killed if the timeout expires, so in order to cleanup properly a well-behaved application should kill the child process and finish communication: proc = subprocess.Popen(...)
try:
    outs, errs = proc.communicate(timeout=15)
except TimeoutExpired:
    proc.kill()
    outs, errs = proc.communicate()
  Note The data read is buffered in memory, so do not use this method if the data size is large or unlimited.   Changed in version 3.3: timeout was added.


Popen.kill()
Kills the child. On POSIX OSs the function sends SIGKILL to the child. On Windows kill() is an alias for terminate().


Popen.pid
The process ID of the child process. Note that if you set the shell argument to True, this is the process ID of the spawned shell.


Popen.poll()
Check if child process has terminated. Set and return returncode attribute. Otherwise, returns None.


Popen.returncode
The child return code, set by poll() and wait() (and indirectly by communicate()). A None value indicates that the process hasn’t terminated yet. A negative value -N indicates that the child was terminated by signal N (POSIX only).


Popen.send_signal(signal)
Sends the signal signal to the child. Do nothing if the process completed.  Note On Windows, SIGTERM is an alias for terminate(). CTRL_C_EVENT and CTRL_BREAK_EVENT can be sent to processes started with a creationflags parameter which includes CREATE_NEW_PROCESS_GROUP.


Popen.stderr
If the stderr argument was PIPE, this attribute is a readable stream object as returned by open(). Reading from the stream provides error output from the child process. If the encoding or errors arguments were specified or the universal_newlines argument was True, the stream is a text stream, otherwise it is a byte stream. If the stderr argument was not PIPE, this attribute is None.


Popen.stdin
If the stdin argument was PIPE, this attribute is a writeable stream object as returned by open(). If the encoding or errors arguments were specified or the universal_newlines argument was True, the stream is a text stream, otherwise it is a byte stream. If the stdin argument was not PIPE, this attribute is None.


Popen.stdout
If the stdout argument was PIPE, this attribute is a readable stream object as returned by open(). Reading from the stream provides output from the child process. If the encoding or errors arguments were specified or the universal_newlines argument was True, the stream is a text stream, otherwise it is a byte stream. If the stdout argument was not PIPE, this attribute is None.


Popen.terminate()
Stop the child. On POSIX OSs the method sends SIGTERM to the child. On Windows the Win32 API function TerminateProcess() is called to stop the child.


Popen.wait(timeout=None)
Wait for child process to terminate. Set and return returncode attribute. If the process does not terminate after timeout seconds, raise a TimeoutExpired exception. It is safe to catch this exception and retry the wait.  Note This will deadlock when using stdout=PIPE or stderr=PIPE and the child process generates enough output to a pipe such that it blocks waiting for the OS pipe buffer to accept more data. Use Popen.communicate() when using pipes to avoid that.   Note The function is implemented using a busy loop (non-blocking call and short sleeps). Use the asyncio module for an asynchronous wait: see asyncio.create_subprocess_exec.   Changed in version 3.3: timeout was added.


subprocess.REALTIME_PRIORITY_CLASS
A Popen creationflags parameter to specify that a new process will have realtime priority. You should almost never use REALTIME_PRIORITY_CLASS, because this interrupts system threads that manage mouse input, keyboard input, and background disk flushing. This class can be appropriate for applications that “talk” directly to hardware or that perform brief tasks that should have limited interruptions.  New in version 3.7.


subprocess.run(args, *, stdin=None, input=None, stdout=None, stderr=None, capture_output=False, shell=False, cwd=None, timeout=None, check=False, encoding=None, errors=None, text=None, env=None, universal_newlines=None, **other_popen_kwargs)
Run the command described by args. Wait for command to complete, then return a CompletedProcess instance. The arguments shown above are merely the most common ones, described below in Frequently Used Arguments (hence the use of keyword-only notation in the abbreviated signature). The full function signature is largely the same as that of the Popen constructor - most of the arguments to this function are passed through to that interface. (timeout, input, check, and capture_output are not.) If capture_output is true, stdout and stderr will be captured. When used, the internal Popen object is automatically created with stdout=PIPE and stderr=PIPE. The stdout and stderr arguments may not be supplied at the same time as capture_output. If you wish to capture and combine both streams into one, use stdout=PIPE and stderr=STDOUT instead of capture_output. The timeout argument is passed to Popen.communicate(). If the timeout expires, the child process will be killed and waited for. The TimeoutExpired exception will be re-raised after the child process has terminated. The input argument is passed to Popen.communicate() and thus to the subprocess’s stdin. If used it must be a byte sequence, or a string if encoding or errors is specified or text is true. When used, the internal Popen object is automatically created with stdin=PIPE, and the stdin argument may not be used as well. If check is true, and the process exits with a non-zero exit code, a CalledProcessError exception will be raised. Attributes of that exception hold the arguments, the exit code, and stdout and stderr if they were captured. If encoding or errors are specified, or text is true, file objects for stdin, stdout and stderr are opened in text mode using the specified encoding and errors or the io.TextIOWrapper default. The universal_newlines argument is equivalent to text and is provided for backwards compatibility. By default, file objects are opened in binary mode. If env is not None, it must be a mapping that defines the environment variables for the new process; these are used instead of the default behavior of inheriting the current process’ environment. It is passed directly to Popen. Examples: >>> subprocess.run(["ls", "-l"])  # doesn't capture output
CompletedProcess(args=['ls', '-l'], returncode=0)

>>> subprocess.run("exit 1", shell=True, check=True)
Traceback (most recent call last):
  ...
subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

>>> subprocess.run(["ls", "-l", "/dev/null"], capture_output=True)
CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n', stderr=b'')
  New in version 3.5.   Changed in version 3.6: Added encoding and errors parameters   Changed in version 3.7: Added the text parameter, as a more understandable alias of universal_newlines. Added the capture_output parameter.


subprocess.STARTF_USESHOWWINDOW
Specifies that the STARTUPINFO.wShowWindow attribute contains additional information.


subprocess.STARTF_USESTDHANDLES
Specifies that the STARTUPINFO.hStdInput, STARTUPINFO.hStdOutput, and STARTUPINFO.hStdError attributes contain additional information.


class subprocess.STARTUPINFO(*, dwFlags=0, hStdInput=None, hStdOutput=None, hStdError=None, wShowWindow=0, lpAttributeList=None)
Partial support of the Windows STARTUPINFO structure is used for Popen creation. The following attributes can be set by passing them as keyword-only arguments.  Changed in version 3.7: Keyword-only argument support was added.
dwFlags
A bit field that determines whether certain STARTUPINFO attributes are used when the process creates a window. si = subprocess.STARTUPINFO()
si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW

hStdInput
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard input handle for the process. If STARTF_USESTDHANDLES is not specified, the default for standard input is the keyboard buffer.

hStdOutput
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard output handle for the process. Otherwise, this attribute is ignored and the default for standard output is the console window’s buffer.

hStdError
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard error handle for the process. Otherwise, this attribute is ignored and the default for standard error is the console window’s buffer.

wShowWindow
If dwFlags specifies STARTF_USESHOWWINDOW, this attribute can be any of the values that can be specified in the nCmdShow parameter for the ShowWindow function, except for SW_SHOWDEFAULT. Otherwise, this attribute is ignored. SW_HIDE is provided for this attribute. It is used when Popen is called with shell=True.

lpAttributeList
A dictionary of additional attributes for process creation as given in STARTUPINFOEX, see UpdateProcThreadAttribute. Supported attributes:  handle_list

Sequence of handles that will be inherited. close_fds must be true if non-empty. The handles must be temporarily made inheritable by os.set_handle_inheritable() when passed to the Popen constructor, else OSError will be raised with Windows error ERROR_INVALID_PARAMETER (87).  Warning In a multithreaded process, use caution to avoid leaking handles that are marked inheritable when combining this feature with concurrent calls to other process creation functions that inherit all handles such as os.system(). This also applies to standard handle redirection, which temporarily creates inheritable handles.     New in version 3.7.


dwFlags
A bit field that determines whether certain STARTUPINFO attributes are used when the process creates a window. si = subprocess.STARTUPINFO()
si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW


hStdError
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard error handle for the process. Otherwise, this attribute is ignored and the default for standard error is the console window’s buffer.


hStdInput
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard input handle for the process. If STARTF_USESTDHANDLES is not specified, the default for standard input is the keyboard buffer.


hStdOutput
If dwFlags specifies STARTF_USESTDHANDLES, this attribute is the standard output handle for the process. Otherwise, this attribute is ignored and the default for standard output is the console window’s buffer.


lpAttributeList
A dictionary of additional attributes for process creation as given in STARTUPINFOEX, see UpdateProcThreadAttribute. Supported attributes:  handle_list

Sequence of handles that will be inherited. close_fds must be true if non-empty. The handles must be temporarily made inheritable by os.set_handle_inheritable() when passed to the Popen constructor, else OSError will be raised with Windows error ERROR_INVALID_PARAMETER (87).  Warning In a multithreaded process, use caution to avoid leaking handles that are marked inheritable when combining this feature with concurrent calls to other process creation functions that inherit all handles such as os.system(). This also applies to standard handle redirection, which temporarily creates inheritable handles.     New in version 3.7.


wShowWindow
If dwFlags specifies STARTF_USESHOWWINDOW, this attribute can be any of the values that can be specified in the nCmdShow parameter for the ShowWindow function, except for SW_SHOWDEFAULT. Otherwise, this attribute is ignored. SW_HIDE is provided for this attribute. It is used when Popen is called with shell=True.


subprocess.STDOUT
Special value that can be used as the stderr argument to Popen and indicates that standard error should go into the same handle as standard output.


subprocess.STD_ERROR_HANDLE
The standard error device. Initially, this is the active console screen buffer, CONOUT$.


subprocess.STD_INPUT_HANDLE
The standard input device. Initially, this is the console input buffer, CONIN$.


subprocess.STD_OUTPUT_HANDLE
The standard output device. Initially, this is the active console screen buffer, CONOUT$.


exception subprocess.SubprocessError
Base class for all other exceptions from this module.  New in version 3.3.


subprocess.SW_HIDE
Hides the window. Another window will be activated.