chunk — Read IFF chunked data Source code: Lib/chunk.py This module provides an interface for reading files that use EA IFF 85 chunks. 1 This format is used in at least the Audio Interchange File Format (AIFF/AIFF-C) and the Real Media File Format (RMFF). The WAVE audio file format is closely related and can also be read using this module. A chunk has the following structure:
Offset Length Contents
0 4 Chunk ID
4 4 Size of chunk in big-endian byte order, not including the header
8 n Data bytes, where n is the size given in the preceding field
8 + n 0 or 1 Pad byte needed if n is odd and chunk alignment is used   The ID is a 4-byte string which identifies the type of chunk. The size field (a 32-bit value, encoded using big-endian byte order) gives the size of the chunk data, not including the 8-byte header. Usually an IFF-type file consists of one or more chunks. The proposed usage of the Chunk class defined here is to instantiate an instance at the start of each chunk and read from the instance until it reaches the end, after which a new instance can be instantiated. At the end of the file, creating a new instance will fail with an EOFError exception.
class chunk.Chunk(file, align=True, bigendian=True, inclheader=False)
Class which represents a chunk. The file argument is expected to be a file-like object. An instance of this class is specifically allowed. The only method that is needed is read(). If the methods seek() and tell() are present and don’t raise an exception, they are also used. If these methods are present and raise an exception, they are expected to not have altered the object. If the optional argument align is true, chunks are assumed to be aligned on 2-byte boundaries. If align is false, no alignment is assumed. The default value is true. If the optional argument bigendian is false, the chunk size is assumed to be in little-endian order. This is needed for WAVE audio files. The default value is true. If the optional argument inclheader is true, the size given in the chunk header includes the size of the header. The default value is false. A Chunk object supports the following methods:
getname()
Returns the name (ID) of the chunk. This is the first 4 bytes of the chunk.

getsize()
Returns the size of the chunk.

close()
Close and skip to the end of the chunk. This does not close the underlying file.
 The remaining methods will raise OSError if called after the close() method has been called. Before Python 3.3, they used to raise IOError, now an alias of OSError.
isatty()
Returns False.

seek(pos, whence=0)
Set the chunk’s current position. The whence argument is optional and defaults to 0 (absolute file positioning); other values are 1 (seek relative to the current position) and 2 (seek relative to the file’s end). There is no return value. If the underlying file does not allow seek, only forward seeks are allowed.

tell()
Return the current position into the chunk.

read(size=-1)
Read at most size bytes from the chunk (less if the read hits the end of the chunk before obtaining size bytes). If the size argument is negative or omitted, read all data until the end of the chunk. An empty bytes object is returned when the end of the chunk is encountered immediately.

skip()
Skip to the end of the chunk. All further calls to read() for the chunk will return b''. If you are not interested in the contents of the chunk, this method should be called so that the file points to the start of the next chunk.

 Footnotes
1
“EA IFF 85” Standard for Interchange Format Files, Jerry Morrison, Electronic Arts, January 1985.


class chunk.Chunk(file, align=True, bigendian=True, inclheader=False)
Class which represents a chunk. The file argument is expected to be a file-like object. An instance of this class is specifically allowed. The only method that is needed is read(). If the methods seek() and tell() are present and don’t raise an exception, they are also used. If these methods are present and raise an exception, they are expected to not have altered the object. If the optional argument align is true, chunks are assumed to be aligned on 2-byte boundaries. If align is false, no alignment is assumed. The default value is true. If the optional argument bigendian is false, the chunk size is assumed to be in little-endian order. This is needed for WAVE audio files. The default value is true. If the optional argument inclheader is true, the size given in the chunk header includes the size of the header. The default value is false. A Chunk object supports the following methods:
getname()
Returns the name (ID) of the chunk. This is the first 4 bytes of the chunk.

getsize()
Returns the size of the chunk.

close()
Close and skip to the end of the chunk. This does not close the underlying file.
 The remaining methods will raise OSError if called after the close() method has been called. Before Python 3.3, they used to raise IOError, now an alias of OSError.
isatty()
Returns False.

seek(pos, whence=0)
Set the chunk’s current position. The whence argument is optional and defaults to 0 (absolute file positioning); other values are 1 (seek relative to the current position) and 2 (seek relative to the file’s end). There is no return value. If the underlying file does not allow seek, only forward seeks are allowed.

tell()
Return the current position into the chunk.

read(size=-1)
Read at most size bytes from the chunk (less if the read hits the end of the chunk before obtaining size bytes). If the size argument is negative or omitted, read all data until the end of the chunk. An empty bytes object is returned when the end of the chunk is encountered immediately.

skip()
Skip to the end of the chunk. All further calls to read() for the chunk will return b''. If you are not interested in the contents of the chunk, this method should be called so that the file points to the start of the next chunk.


close()
Close and skip to the end of the chunk. This does not close the underlying file.


getname()
Returns the name (ID) of the chunk. This is the first 4 bytes of the chunk.


getsize()
Returns the size of the chunk.


read(size=-1)
Read at most size bytes from the chunk (less if the read hits the end of the chunk before obtaining size bytes). If the size argument is negative or omitted, read all data until the end of the chunk. An empty bytes object is returned when the end of the chunk is encountered immediately.


seek(pos, whence=0)
Set the chunk’s current position. The whence argument is optional and defaults to 0 (absolute file positioning); other values are 1 (seek relative to the current position) and 2 (seek relative to the file’s end). There is no return value. If the underlying file does not allow seek, only forward seeks are allowed.


skip()
Skip to the end of the chunk. All further calls to read() for the chunk will return b''. If you are not interested in the contents of the chunk, this method should be called so that the file points to the start of the next chunk.


tell()
Return the current position into the chunk.


class.mro()
This method can be overridden by a metaclass to customize the method resolution order for its instances. It is called at class instantiation, and its result is stored in __mro__.


class.__bases__
The tuple of base classes of a class object.


class.__mro__
This attribute is a tuple of classes that are considered when looking for base classes during method resolution.


class.__subclasses__()
Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. The list is in definition order. Example: >>> int.__subclasses__()
[<class 'bool'>]


@classmethod
Transform a method into a class method. A class method receives the class as implicit first argument, just like an instance method receives the instance. To declare a class method, use this idiom: class C:
    @classmethod
    def f(cls, arg1, arg2, ...): ...
 The @classmethod form is a function decorator – see Function definitions for details. A class method can be called either on the class (such as C.f()) or on an instance (such as C().f()). The instance is ignored except for its class. If a class method is called for a derived class, the derived class object is passed as the implied first argument. Class methods are different than C++ or Java static methods. If you want those, see staticmethod() in this section. For more information on class methods, see The standard type hierarchy.  Changed in version 3.9: Class methods can now wrap other descriptors such as property().


cmath — Mathematical functions for complex numbers This module provides access to mathematical functions for complex numbers. The functions in this module accept integers, floating-point numbers or complex numbers as arguments. They will also accept any Python object that has either a __complex__() or a __float__() method: these methods are used to convert the object to a complex or floating-point number, respectively, and the function is then applied to the result of the conversion.  Note On platforms with hardware and system-level support for signed zeros, functions involving branch cuts are continuous on both sides of the branch cut: the sign of the zero distinguishes one side of the branch cut from the other. On platforms that do not support signed zeros the continuity is as specified below.  Conversions to and from polar coordinates A Python complex number z is stored internally using rectangular or Cartesian coordinates. It is completely determined by its real part z.real and its imaginary part z.imag. In other words: z == z.real + z.imag*1j
 Polar coordinates give an alternative way to represent a complex number. In polar coordinates, a complex number z is defined by the modulus r and the phase angle phi. The modulus r is the distance from z to the origin, while the phase phi is the counterclockwise angle, measured in radians, from the positive x-axis to the line segment that joins the origin to z. The following functions can be used to convert from the native rectangular coordinates to polar coordinates and back.
cmath.phase(x)
Return the phase of x (also known as the argument of x), as a float. phase(x) is equivalent to math.atan2(x.imag,
x.real). The result lies in the range [-π, π], and the branch cut for this operation lies along the negative real axis, continuous from above. On systems with support for signed zeros (which includes most systems in current use), this means that the sign of the result is the same as the sign of x.imag, even when x.imag is zero: >>> phase(complex(-1.0, 0.0))
3.141592653589793
>>> phase(complex(-1.0, -0.0))
-3.141592653589793

  Note The modulus (absolute value) of a complex number x can be computed using the built-in abs() function. There is no separate cmath module function for this operation.
cmath.polar(x)
Return the representation of x in polar coordinates. Returns a pair (r, phi) where r is the modulus of x and phi is the phase of x. polar(x) is equivalent to (abs(x),
phase(x)).

cmath.rect(r, phi)
Return the complex number x with polar coordinates r and phi. Equivalent to r * (math.cos(phi) + math.sin(phi)*1j).
 Power and logarithmic functions
cmath.exp(x)
Return e raised to the power x, where e is the base of natural logarithms.

cmath.log(x[, base])
Returns the logarithm of x to the given base. If the base is not specified, returns the natural logarithm of x. There is one branch cut, from 0 along the negative real axis to -∞, continuous from above.

cmath.log10(x)
Return the base-10 logarithm of x. This has the same branch cut as log().

cmath.sqrt(x)
Return the square root of x. This has the same branch cut as log().
 Trigonometric functions
cmath.acos(x)
Return the arc cosine of x. There are two branch cuts: One extends right from 1 along the real axis to ∞, continuous from below. The other extends left from -1 along the real axis to -∞, continuous from above.

cmath.asin(x)
Return the arc sine of x. This has the same branch cuts as acos().

cmath.atan(x)
Return the arc tangent of x. There are two branch cuts: One extends from 1j along the imaginary axis to ∞j, continuous from the right. The other extends from -1j along the imaginary axis to -∞j, continuous from the left.

cmath.cos(x)
Return the cosine of x.

cmath.sin(x)
Return the sine of x.

cmath.tan(x)
Return the tangent of x.
 Hyperbolic functions
cmath.acosh(x)
Return the inverse hyperbolic cosine of x. There is one branch cut, extending left from 1 along the real axis to -∞, continuous from above.

cmath.asinh(x)
Return the inverse hyperbolic sine of x. There are two branch cuts: One extends from 1j along the imaginary axis to ∞j, continuous from the right. The other extends from -1j along the imaginary axis to -∞j, continuous from the left.

cmath.atanh(x)
Return the inverse hyperbolic tangent of x. There are two branch cuts: One extends from 1 along the real axis to ∞, continuous from below. The other extends from -1 along the real axis to -∞, continuous from above.

cmath.cosh(x)
Return the hyperbolic cosine of x.

cmath.sinh(x)
Return the hyperbolic sine of x.

cmath.tanh(x)
Return the hyperbolic tangent of x.
 Classification functions
cmath.isfinite(x)
Return True if both the real and imaginary parts of x are finite, and False otherwise.  New in version 3.2.

cmath.isinf(x)
Return True if either the real or the imaginary part of x is an infinity, and False otherwise.

cmath.isnan(x)
Return True if either the real or the imaginary part of x is a NaN, and False otherwise.

cmath.isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0)
Return True if the values a and b are close to each other and False otherwise. Whether or not two values are considered close is determined according to given absolute and relative tolerances. rel_tol is the relative tolerance – it is the maximum allowed difference between a and b, relative to the larger absolute value of a or b. For example, to set a tolerance of 5%, pass rel_tol=0.05. The default tolerance is 1e-09, which assures that the two values are the same within about 9 decimal digits. rel_tol must be greater than zero. abs_tol is the minimum absolute tolerance – useful for comparisons near zero. abs_tol must be at least zero. If no errors occur, the result will be: abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol). The IEEE 754 special values of NaN, inf, and -inf will be handled according to IEEE rules. Specifically, NaN is not considered close to any other value, including NaN. inf and -inf are only considered close to themselves.  New in version 3.5.   See also PEP 485 – A function for testing approximate equality
 Constants
cmath.pi
The mathematical constant π, as a float.

cmath.e
The mathematical constant e, as a float.

cmath.tau
The mathematical constant τ, as a float.  New in version 3.6.

cmath.inf
Floating-point positive infinity. Equivalent to float('inf').  New in version 3.6.

cmath.infj
Complex number with zero real part and positive infinity imaginary part. Equivalent to complex(0.0, float('inf')).  New in version 3.6.

cmath.nan
A floating-point “not a number” (NaN) value. Equivalent to float('nan').  New in version 3.6.

cmath.nanj
Complex number with zero real part and NaN imaginary part. Equivalent to complex(0.0, float('nan')).  New in version 3.6.
 Note that the selection of functions is similar, but not identical, to that in module math. The reason for having two modules is that some users aren’t interested in complex numbers, and perhaps don’t even know what they are. They would rather have math.sqrt(-1) raise an exception than return a complex number. Also note that the functions defined in cmath always return a complex number, even if the answer can be expressed as a real number (in which case the complex number has an imaginary part of zero). A note on branch cuts: They are curves along which the given function fails to be continuous. They are a necessary feature of many complex functions. It is assumed that if you need to compute with complex functions, you will understand about branch cuts. Consult almost any (not too elementary) book on complex variables for enlightenment. For information of the proper choice of branch cuts for numerical purposes, a good reference should be the following:  See also Kahan, W: Branch cuts for complex elementary functions; or, Much ado about nothing’s sign bit. In Iserles, A., and Powell, M. (eds.), The state of the art in numerical analysis. Clarendon Press (1987) pp165–211.


cmath.acos(x)
Return the arc cosine of x. There are two branch cuts: One extends right from 1 along the real axis to ∞, continuous from below. The other extends left from -1 along the real axis to -∞, continuous from above.


cmath.acosh(x)
Return the inverse hyperbolic cosine of x. There is one branch cut, extending left from 1 along the real axis to -∞, continuous from above.


cmath.asin(x)
Return the arc sine of x. This has the same branch cuts as acos().


cmath.asinh(x)
Return the inverse hyperbolic sine of x. There are two branch cuts: One extends from 1j along the imaginary axis to ∞j, continuous from the right. The other extends from -1j along the imaginary axis to -∞j, continuous from the left.


cmath.atan(x)
Return the arc tangent of x. There are two branch cuts: One extends from 1j along the imaginary axis to ∞j, continuous from the right. The other extends from -1j along the imaginary axis to -∞j, continuous from the left.


cmath.atanh(x)
Return the inverse hyperbolic tangent of x. There are two branch cuts: One extends from 1 along the real axis to ∞, continuous from below. The other extends from -1 along the real axis to -∞, continuous from above.


cmath.cosh(x)
Return the hyperbolic cosine of x.


cmath.e
The mathematical constant e, as a float.


cmath.exp(x)
Return e raised to the power x, where e is the base of natural logarithms.


cmath.inf
Floating-point positive infinity. Equivalent to float('inf').  New in version 3.6.


cmath.infj
Complex number with zero real part and positive infinity imaginary part. Equivalent to complex(0.0, float('inf')).  New in version 3.6.


cmath.isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0)
Return True if the values a and b are close to each other and False otherwise. Whether or not two values are considered close is determined according to given absolute and relative tolerances. rel_tol is the relative tolerance – it is the maximum allowed difference between a and b, relative to the larger absolute value of a or b. For example, to set a tolerance of 5%, pass rel_tol=0.05. The default tolerance is 1e-09, which assures that the two values are the same within about 9 decimal digits. rel_tol must be greater than zero. abs_tol is the minimum absolute tolerance – useful for comparisons near zero. abs_tol must be at least zero. If no errors occur, the result will be: abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol). The IEEE 754 special values of NaN, inf, and -inf will be handled according to IEEE rules. Specifically, NaN is not considered close to any other value, including NaN. inf and -inf are only considered close to themselves.  New in version 3.5.   See also PEP 485 – A function for testing approximate equality


cmath.isfinite(x)
Return True if both the real and imaginary parts of x are finite, and False otherwise.  New in version 3.2.


cmath.isinf(x)
Return True if either the real or the imaginary part of x is an infinity, and False otherwise.


cmath.isnan(x)
Return True if either the real or the imaginary part of x is a NaN, and False otherwise.


cmath.log(x[, base])
Returns the logarithm of x to the given base. If the base is not specified, returns the natural logarithm of x. There is one branch cut, from 0 along the negative real axis to -∞, continuous from above.


cmath.log10(x)
Return the base-10 logarithm of x. This has the same branch cut as log().


cmath.nan
A floating-point “not a number” (NaN) value. Equivalent to float('nan').  New in version 3.6.


cmath.nanj
Complex number with zero real part and NaN imaginary part. Equivalent to complex(0.0, float('nan')).  New in version 3.6.


cmath.phase(x)
Return the phase of x (also known as the argument of x), as a float. phase(x) is equivalent to math.atan2(x.imag,
x.real). The result lies in the range [-π, π], and the branch cut for this operation lies along the negative real axis, continuous from above. On systems with support for signed zeros (which includes most systems in current use), this means that the sign of the result is the same as the sign of x.imag, even when x.imag is zero: >>> phase(complex(-1.0, 0.0))
3.141592653589793
>>> phase(complex(-1.0, -0.0))
-3.141592653589793


cmath.pi
The mathematical constant π, as a float.


cmath.polar(x)
Return the representation of x in polar coordinates. Returns a pair (r, phi) where r is the modulus of x and phi is the phase of x. polar(x) is equivalent to (abs(x),
phase(x)).


cmath.rect(r, phi)
Return the complex number x with polar coordinates r and phi. Equivalent to r * (math.cos(phi) + math.sin(phi)*1j).


cmath.sinh(x)
Return the hyperbolic sine of x.


cmath.sqrt(x)
Return the square root of x. This has the same branch cut as log().


cmath.tanh(x)
Return the hyperbolic tangent of x.


cmath.tau
The mathematical constant τ, as a float.  New in version 3.6.


cmd — Support for line-oriented command interpreters Source code: Lib/cmd.py The Cmd class provides a simple framework for writing line-oriented command interpreters. These are often useful for test harnesses, administrative tools, and prototypes that will later be wrapped in a more sophisticated interface.
class cmd.Cmd(completekey='tab', stdin=None, stdout=None)
A Cmd instance or subclass instance is a line-oriented interpreter framework. There is no good reason to instantiate Cmd itself; rather, it’s useful as a superclass of an interpreter class you define yourself in order to inherit Cmd’s methods and encapsulate action methods. The optional argument completekey is the readline name of a completion key; it defaults to Tab. If completekey is not None and readline is available, command completion is done automatically. The optional arguments stdin and stdout specify the input and output file objects that the Cmd instance or subclass instance will use for input and output. If not specified, they will default to sys.stdin and sys.stdout. If you want a given stdin to be used, make sure to set the instance’s use_rawinput attribute to False, otherwise stdin will be ignored.
 Cmd Objects A Cmd instance has the following methods:
Cmd.cmdloop(intro=None)
Repeatedly issue a prompt, accept input, parse an initial prefix off the received input, and dispatch to action methods, passing them the remainder of the line as argument. The optional argument is a banner or intro string to be issued before the first prompt (this overrides the intro class attribute). If the readline module is loaded, input will automatically inherit bash-like history-list editing (e.g. Control-P scrolls back to the last command, Control-N forward to the next one, Control-F moves the cursor to the right non-destructively, Control-B moves the cursor to the left non-destructively, etc.). An end-of-file on input is passed back as the string 'EOF'. An interpreter instance will recognize a command name foo if and only if it has a method do_foo(). As a special case, a line beginning with the character '?' is dispatched to the method do_help(). As another special case, a line beginning with the character '!' is dispatched to the method do_shell() (if such a method is defined). This method will return when the postcmd() method returns a true value. The stop argument to postcmd() is the return value from the command’s corresponding do_*() method. If completion is enabled, completing commands will be done automatically, and completing of commands args is done by calling complete_foo() with arguments text, line, begidx, and endidx. text is the string prefix we are attempting to match: all returned matches must begin with it. line is the current input line with leading whitespace removed, begidx and endidx are the beginning and ending indexes of the prefix text, which could be used to provide different completion depending upon which position the argument is in. All subclasses of Cmd inherit a predefined do_help(). This method, called with an argument 'bar', invokes the corresponding method help_bar(), and if that is not present, prints the docstring of do_bar(), if available. With no argument, do_help() lists all available help topics (that is, all commands with corresponding help_*() methods or commands that have docstrings), and also lists any undocumented commands.

Cmd.onecmd(str)
Interpret the argument as though it had been typed in response to the prompt. This may be overridden, but should not normally need to be; see the precmd() and postcmd() methods for useful execution hooks. The return value is a flag indicating whether interpretation of commands by the interpreter should stop. If there is a do_*() method for the command str, the return value of that method is returned, otherwise the return value from the default() method is returned.

Cmd.emptyline()
Method called when an empty line is entered in response to the prompt. If this method is not overridden, it repeats the last nonempty command entered.

Cmd.default(line)
Method called on an input line when the command prefix is not recognized. If this method is not overridden, it prints an error message and returns.

Cmd.completedefault(text, line, begidx, endidx)
Method called to complete an input line when no command-specific complete_*() method is available. By default, it returns an empty list.

Cmd.precmd(line)
Hook method executed just before the command line line is interpreted, but after the input prompt is generated and issued. This method is a stub in Cmd; it exists to be overridden by subclasses. The return value is used as the command which will be executed by the onecmd() method; the precmd() implementation may re-write the command or simply return line unchanged.

Cmd.postcmd(stop, line)
Hook method executed just after a command dispatch is finished. This method is a stub in Cmd; it exists to be overridden by subclasses. line is the command line which was executed, and stop is a flag which indicates whether execution will be terminated after the call to postcmd(); this will be the return value of the onecmd() method. The return value of this method will be used as the new value for the internal flag which corresponds to stop; returning false will cause interpretation to continue.

Cmd.preloop()
Hook method executed once when cmdloop() is called. This method is a stub in Cmd; it exists to be overridden by subclasses.

Cmd.postloop()
Hook method executed once when cmdloop() is about to return. This method is a stub in Cmd; it exists to be overridden by subclasses.
 Instances of Cmd subclasses have some public instance variables:
Cmd.prompt
The prompt issued to solicit input.

Cmd.identchars
The string of characters accepted for the command prefix.

Cmd.lastcmd
The last nonempty command prefix seen.

Cmd.cmdqueue
A list of queued input lines. The cmdqueue list is checked in cmdloop() when new input is needed; if it is nonempty, its elements will be processed in order, as if entered at the prompt.

Cmd.intro
A string to issue as an intro or banner. May be overridden by giving the cmdloop() method an argument.

Cmd.doc_header
The header to issue if the help output has a section for documented commands.

Cmd.misc_header
The header to issue if the help output has a section for miscellaneous help topics (that is, there are help_*() methods without corresponding do_*() methods).

Cmd.undoc_header
The header to issue if the help output has a section for undocumented commands (that is, there are do_*() methods without corresponding help_*() methods).

Cmd.ruler
The character used to draw separator lines under the help-message headers. If empty, no ruler line is drawn. It defaults to '='.

Cmd.use_rawinput
A flag, defaulting to true. If true, cmdloop() uses input() to display a prompt and read the next command; if false, sys.stdout.write() and sys.stdin.readline() are used. (This means that by importing readline, on systems that support it, the interpreter will automatically support Emacs-like line editing and command-history keystrokes.)
 Cmd Example The cmd module is mainly useful for building custom shells that let a user work with a program interactively. This section presents a simple example of how to build a shell around a few of the commands in the turtle module. Basic turtle commands such as forward() are added to a Cmd subclass with method named do_forward(). The argument is converted to a number and dispatched to the turtle module. The docstring is used in the help utility provided by the shell. The example also includes a basic record and playback facility implemented with the precmd() method which is responsible for converting the input to lowercase and writing the commands to a file. The do_playback() method reads the file and adds the recorded commands to the cmdqueue for immediate playback: import cmd, sys
from turtle import *

class TurtleShell(cmd.Cmd):
    intro = 'Welcome to the turtle shell.   Type help or ? to list commands.\n'
    prompt = '(turtle) '
    file = None

    # ----- basic turtle commands -----
    def do_forward(self, arg):
        'Move the turtle forward by the specified distance:  FORWARD 10'
        forward(*parse(arg))
    def do_right(self, arg):
        'Turn turtle right by given number of degrees:  RIGHT 20'
        right(*parse(arg))
    def do_left(self, arg):
        'Turn turtle left by given number of degrees:  LEFT 90'
        left(*parse(arg))
    def do_goto(self, arg):
        'Move turtle to an absolute position with changing orientation.  GOTO 100 200'
        goto(*parse(arg))
    def do_home(self, arg):
        'Return turtle to the home position:  HOME'
        home()
    def do_circle(self, arg):
        'Draw circle with given radius an options extent and steps:  CIRCLE 50'
        circle(*parse(arg))
    def do_position(self, arg):
        'Print the current turtle position:  POSITION'
        print('Current position is %d %d\n' % position())
    def do_heading(self, arg):
        'Print the current turtle heading in degrees:  HEADING'
        print('Current heading is %d\n' % (heading(),))
    def do_color(self, arg):
        'Set the color:  COLOR BLUE'
        color(arg.lower())
    def do_undo(self, arg):
        'Undo (repeatedly) the last turtle action(s):  UNDO'
    def do_reset(self, arg):
        'Clear the screen and return turtle to center:  RESET'
        reset()
    def do_bye(self, arg):
        'Stop recording, close the turtle window, and exit:  BYE'
        print('Thank you for using Turtle')
        self.close()
        bye()
        return True

    # ----- record and playback -----
    def do_record(self, arg):
        'Save future commands to filename:  RECORD rose.cmd'
        self.file = open(arg, 'w')
    def do_playback(self, arg):
        'Playback commands from a file:  PLAYBACK rose.cmd'
        self.close()
        with open(arg) as f:
            self.cmdqueue.extend(f.read().splitlines())
    def precmd(self, line):
        line = line.lower()
        if self.file and 'playback' not in line:
            print(line, file=self.file)
        return line
    def close(self):
        if self.file:
            self.file.close()
            self.file = None

def parse(arg):
    'Convert a series of zero or more numbers to an argument tuple'
    return tuple(map(int, arg.split()))

if __name__ == '__main__':
    TurtleShell().cmdloop()
 Here is a sample session with the turtle shell showing the help functions, using blank lines to repeat commands, and the simple record and playback facility: Welcome to the turtle shell.   Type help or ? to list commands.

(turtle) ?

Documented commands (type help <topic>):
========================================
bye     color    goto     home  playback  record  right
circle  forward  heading  left  position  reset   undo

(turtle) help forward
Move the turtle forward by the specified distance:  FORWARD 10
(turtle) record spiral.cmd
(turtle) position
Current position is 0 0

(turtle) heading
Current heading is 0

(turtle) reset
(turtle) circle 20
(turtle) right 30
(turtle) circle 40
(turtle) right 30
(turtle) circle 60
(turtle) right 30
(turtle) circle 80
(turtle) right 30
(turtle) circle 100
(turtle) right 30
(turtle) circle 120
(turtle) right 30
(turtle) circle 120
(turtle) heading
Current heading is 180

(turtle) forward 100
(turtle)
(turtle) right 90
(turtle) forward 100
(turtle)
(turtle) right 90
(turtle) forward 400
(turtle) right 90
(turtle) forward 500
(turtle) right 90
(turtle) forward 400
(turtle) right 90
(turtle) forward 300
(turtle) playback spiral.cmd
Current position is 0 0

Current heading is 0

Current heading is 180

(turtle) bye
Thank you for using Turtle


class cmd.Cmd(completekey='tab', stdin=None, stdout=None)
A Cmd instance or subclass instance is a line-oriented interpreter framework. There is no good reason to instantiate Cmd itself; rather, it’s useful as a superclass of an interpreter class you define yourself in order to inherit Cmd’s methods and encapsulate action methods. The optional argument completekey is the readline name of a completion key; it defaults to Tab. If completekey is not None and readline is available, command completion is done automatically. The optional arguments stdin and stdout specify the input and output file objects that the Cmd instance or subclass instance will use for input and output. If not specified, they will default to sys.stdin and sys.stdout. If you want a given stdin to be used, make sure to set the instance’s use_rawinput attribute to False, otherwise stdin will be ignored.


Cmd.cmdloop(intro=None)
Repeatedly issue a prompt, accept input, parse an initial prefix off the received input, and dispatch to action methods, passing them the remainder of the line as argument. The optional argument is a banner or intro string to be issued before the first prompt (this overrides the intro class attribute). If the readline module is loaded, input will automatically inherit bash-like history-list editing (e.g. Control-P scrolls back to the last command, Control-N forward to the next one, Control-F moves the cursor to the right non-destructively, Control-B moves the cursor to the left non-destructively, etc.). An end-of-file on input is passed back as the string 'EOF'. An interpreter instance will recognize a command name foo if and only if it has a method do_foo(). As a special case, a line beginning with the character '?' is dispatched to the method do_help(). As another special case, a line beginning with the character '!' is dispatched to the method do_shell() (if such a method is defined). This method will return when the postcmd() method returns a true value. The stop argument to postcmd() is the return value from the command’s corresponding do_*() method. If completion is enabled, completing commands will be done automatically, and completing of commands args is done by calling complete_foo() with arguments text, line, begidx, and endidx. text is the string prefix we are attempting to match: all returned matches must begin with it. line is the current input line with leading whitespace removed, begidx and endidx are the beginning and ending indexes of the prefix text, which could be used to provide different completion depending upon which position the argument is in. All subclasses of Cmd inherit a predefined do_help(). This method, called with an argument 'bar', invokes the corresponding method help_bar(), and if that is not present, prints the docstring of do_bar(), if available. With no argument, do_help() lists all available help topics (that is, all commands with corresponding help_*() methods or commands that have docstrings), and also lists any undocumented commands.


Cmd.cmdqueue
A list of queued input lines. The cmdqueue list is checked in cmdloop() when new input is needed; if it is nonempty, its elements will be processed in order, as if entered at the prompt.


Cmd.completedefault(text, line, begidx, endidx)
Method called to complete an input line when no command-specific complete_*() method is available. By default, it returns an empty list.


Cmd.default(line)
Method called on an input line when the command prefix is not recognized. If this method is not overridden, it prints an error message and returns.


Cmd.doc_header
The header to issue if the help output has a section for documented commands.


Cmd.emptyline()
Method called when an empty line is entered in response to the prompt. If this method is not overridden, it repeats the last nonempty command entered.


Cmd.identchars
The string of characters accepted for the command prefix.


Cmd.intro
A string to issue as an intro or banner. May be overridden by giving the cmdloop() method an argument.


Cmd.lastcmd
The last nonempty command prefix seen.


Cmd.misc_header
The header to issue if the help output has a section for miscellaneous help topics (that is, there are help_*() methods without corresponding do_*() methods).


Cmd.onecmd(str)
Interpret the argument as though it had been typed in response to the prompt. This may be overridden, but should not normally need to be; see the precmd() and postcmd() methods for useful execution hooks. The return value is a flag indicating whether interpretation of commands by the interpreter should stop. If there is a do_*() method for the command str, the return value of that method is returned, otherwise the return value from the default() method is returned.


Cmd.postcmd(stop, line)
Hook method executed just after a command dispatch is finished. This method is a stub in Cmd; it exists to be overridden by subclasses. line is the command line which was executed, and stop is a flag which indicates whether execution will be terminated after the call to postcmd(); this will be the return value of the onecmd() method. The return value of this method will be used as the new value for the internal flag which corresponds to stop; returning false will cause interpretation to continue.


Cmd.postloop()
Hook method executed once when cmdloop() is about to return. This method is a stub in Cmd; it exists to be overridden by subclasses.


Cmd.precmd(line)
Hook method executed just before the command line line is interpreted, but after the input prompt is generated and issued. This method is a stub in Cmd; it exists to be overridden by subclasses. The return value is used as the command which will be executed by the onecmd() method; the precmd() implementation may re-write the command or simply return line unchanged.


Cmd.preloop()
Hook method executed once when cmdloop() is called. This method is a stub in Cmd; it exists to be overridden by subclasses.


Cmd.prompt
The prompt issued to solicit input.


Cmd.ruler
The character used to draw separator lines under the help-message headers. If empty, no ruler line is drawn. It defaults to '='.


Cmd.undoc_header
The header to issue if the help output has a section for undocumented commands (that is, there are do_*() methods without corresponding help_*() methods).


Cmd.use_rawinput
A flag, defaulting to true. If true, cmdloop() uses input() to display a prompt and read the next command; if false, sys.stdout.write() and sys.stdin.readline() are used. (This means that by importing readline, on systems that support it, the interpreter will automatically support Emacs-like line editing and command-history keystrokes.)


code — Interpreter base classes Source code: Lib/code.py The code module provides facilities to implement read-eval-print loops in Python. Two classes and convenience functions are included which can be used to build applications which provide an interactive interpreter prompt.
class code.InteractiveInterpreter(locals=None)
This class deals with parsing and interpreter state (the user’s namespace); it does not deal with input buffering or prompting or input file naming (the filename is always passed in explicitly). The optional locals argument specifies the dictionary in which code will be executed; it defaults to a newly created dictionary with key '__name__' set to '__console__' and key '__doc__' set to None.

class code.InteractiveConsole(locals=None, filename="<console>")
Closely emulate the behavior of the interactive Python interpreter. This class builds on InteractiveInterpreter and adds prompting using the familiar sys.ps1 and sys.ps2, and input buffering.

code.interact(banner=None, readfunc=None, local=None, exitmsg=None)
Convenience function to run a read-eval-print loop. This creates a new instance of InteractiveConsole and sets readfunc to be used as the InteractiveConsole.raw_input() method, if provided. If local is provided, it is passed to the InteractiveConsole constructor for use as the default namespace for the interpreter loop. The interact() method of the instance is then run with banner and exitmsg passed as the banner and exit message to use, if provided. The console object is discarded after use.  Changed in version 3.6: Added exitmsg parameter.

code.compile_command(source, filename="<input>", symbol="single")
This function is useful for programs that want to emulate Python’s interpreter main loop (a.k.a. the read-eval-print loop). The tricky part is to determine when the user has entered an incomplete command that can be completed by entering more text (as opposed to a complete command or a syntax error). This function almost always makes the same decision as the real interpreter main loop. source is the source string; filename is the optional filename from which source was read, defaulting to '<input>'; and symbol is the optional grammar start symbol, which should be 'single' (the default), 'eval' or 'exec'. Returns a code object (the same as compile(source, filename, symbol)) if the command is complete and valid; None if the command is incomplete; raises SyntaxError if the command is complete and contains a syntax error, or raises OverflowError or ValueError if the command contains an invalid literal.
 Interactive Interpreter Objects
InteractiveInterpreter.runsource(source, filename="<input>", symbol="single")
Compile and run some source in the interpreter. Arguments are the same as for compile_command(); the default for filename is '<input>', and for symbol is 'single'. One of several things can happen:  The input is incorrect; compile_command() raised an exception (SyntaxError or OverflowError). A syntax traceback will be printed by calling the showsyntaxerror() method. runsource() returns False. The input is incomplete, and more input is required; compile_command() returned None. runsource() returns True. The input is complete; compile_command() returned a code object. The code is executed by calling the runcode() (which also handles run-time exceptions, except for SystemExit). runsource() returns False.  The return value can be used to decide whether to use sys.ps1 or sys.ps2 to prompt the next line.

InteractiveInterpreter.runcode(code)
Execute a code object. When an exception occurs, showtraceback() is called to display a traceback. All exceptions are caught except SystemExit, which is allowed to propagate. A note about KeyboardInterrupt: this exception may occur elsewhere in this code, and may not always be caught. The caller should be prepared to deal with it.

InteractiveInterpreter.showsyntaxerror(filename=None)
Display the syntax error that just occurred. This does not display a stack trace because there isn’t one for syntax errors. If filename is given, it is stuffed into the exception instead of the default filename provided by Python’s parser, because it always uses '<string>' when reading from a string. The output is written by the write() method.

InteractiveInterpreter.showtraceback()
Display the exception that just occurred. We remove the first stack item because it is within the interpreter object implementation. The output is written by the write() method.  Changed in version 3.5: The full chained traceback is displayed instead of just the primary traceback.

InteractiveInterpreter.write(data)
Write a string to the standard error stream (sys.stderr). Derived classes should override this to provide the appropriate output handling as needed.
 Interactive Console Objects The InteractiveConsole class is a subclass of InteractiveInterpreter, and so offers all the methods of the interpreter objects as well as the following additions.
InteractiveConsole.interact(banner=None, exitmsg=None)
Closely emulate the interactive Python console. The optional banner argument specify the banner to print before the first interaction; by default it prints a banner similar to the one printed by the standard Python interpreter, followed by the class name of the console object in parentheses (so as not to confuse this with the real interpreter – since it’s so close!). The optional exitmsg argument specifies an exit message printed when exiting. Pass the empty string to suppress the exit message. If exitmsg is not given or None, a default message is printed.  Changed in version 3.4: To suppress printing any banner, pass an empty string.   Changed in version 3.6: Print an exit message when exiting.

InteractiveConsole.push(line)
Push a line of source text to the interpreter. The line should not have a trailing newline; it may have internal newlines. The line is appended to a buffer and the interpreter’s runsource() method is called with the concatenated contents of the buffer as source. If this indicates that the command was executed or invalid, the buffer is reset; otherwise, the command is incomplete, and the buffer is left as it was after the line was appended. The return value is True if more input is required, False if the line was dealt with in some way (this is the same as runsource()).

InteractiveConsole.resetbuffer()
Remove any unhandled source text from the input buffer.

InteractiveConsole.raw_input(prompt="")
Write a prompt and read a line. The returned line does not include the trailing newline. When the user enters the EOF key sequence, EOFError is raised. The base implementation reads from sys.stdin; a subclass may replace this with a different implementation.


code.compile_command(source, filename="<input>", symbol="single")
This function is useful for programs that want to emulate Python’s interpreter main loop (a.k.a. the read-eval-print loop). The tricky part is to determine when the user has entered an incomplete command that can be completed by entering more text (as opposed to a complete command or a syntax error). This function almost always makes the same decision as the real interpreter main loop. source is the source string; filename is the optional filename from which source was read, defaulting to '<input>'; and symbol is the optional grammar start symbol, which should be 'single' (the default), 'eval' or 'exec'. Returns a code object (the same as compile(source, filename, symbol)) if the command is complete and valid; None if the command is incomplete; raises SyntaxError if the command is complete and contains a syntax error, or raises OverflowError or ValueError if the command contains an invalid literal.


code.interact(banner=None, readfunc=None, local=None, exitmsg=None)
Convenience function to run a read-eval-print loop. This creates a new instance of InteractiveConsole and sets readfunc to be used as the InteractiveConsole.raw_input() method, if provided. If local is provided, it is passed to the InteractiveConsole constructor for use as the default namespace for the interpreter loop. The interact() method of the instance is then run with banner and exitmsg passed as the banner and exit message to use, if provided. The console object is discarded after use.  Changed in version 3.6: Added exitmsg parameter.


class code.InteractiveConsole(locals=None, filename="<console>")
Closely emulate the behavior of the interactive Python interpreter. This class builds on InteractiveInterpreter and adds prompting using the familiar sys.ps1 and sys.ps2, and input buffering.


InteractiveConsole.interact(banner=None, exitmsg=None)
Closely emulate the interactive Python console. The optional banner argument specify the banner to print before the first interaction; by default it prints a banner similar to the one printed by the standard Python interpreter, followed by the class name of the console object in parentheses (so as not to confuse this with the real interpreter – since it’s so close!). The optional exitmsg argument specifies an exit message printed when exiting. Pass the empty string to suppress the exit message. If exitmsg is not given or None, a default message is printed.  Changed in version 3.4: To suppress printing any banner, pass an empty string.   Changed in version 3.6: Print an exit message when exiting.


InteractiveConsole.push(line)
Push a line of source text to the interpreter. The line should not have a trailing newline; it may have internal newlines. The line is appended to a buffer and the interpreter’s runsource() method is called with the concatenated contents of the buffer as source. If this indicates that the command was executed or invalid, the buffer is reset; otherwise, the command is incomplete, and the buffer is left as it was after the line was appended. The return value is True if more input is required, False if the line was dealt with in some way (this is the same as runsource()).


InteractiveConsole.raw_input(prompt="")
Write a prompt and read a line. The returned line does not include the trailing newline. When the user enters the EOF key sequence, EOFError is raised. The base implementation reads from sys.stdin; a subclass may replace this with a different implementation.


InteractiveConsole.resetbuffer()
Remove any unhandled source text from the input buffer.


class code.InteractiveInterpreter(locals=None)
This class deals with parsing and interpreter state (the user’s namespace); it does not deal with input buffering or prompting or input file naming (the filename is always passed in explicitly). The optional locals argument specifies the dictionary in which code will be executed; it defaults to a newly created dictionary with key '__name__' set to '__console__' and key '__doc__' set to None.


InteractiveInterpreter.runcode(code)
Execute a code object. When an exception occurs, showtraceback() is called to display a traceback. All exceptions are caught except SystemExit, which is allowed to propagate. A note about KeyboardInterrupt: this exception may occur elsewhere in this code, and may not always be caught. The caller should be prepared to deal with it.


InteractiveInterpreter.runsource(source, filename="<input>", symbol="single")
Compile and run some source in the interpreter. Arguments are the same as for compile_command(); the default for filename is '<input>', and for symbol is 'single'. One of several things can happen:  The input is incorrect; compile_command() raised an exception (SyntaxError or OverflowError). A syntax traceback will be printed by calling the showsyntaxerror() method. runsource() returns False. The input is incomplete, and more input is required; compile_command() returned None. runsource() returns True. The input is complete; compile_command() returned a code object. The code is executed by calling the runcode() (which also handles run-time exceptions, except for SystemExit). runsource() returns False.  The return value can be used to decide whether to use sys.ps1 or sys.ps2 to prompt the next line.


InteractiveInterpreter.showsyntaxerror(filename=None)
Display the syntax error that just occurred. This does not display a stack trace because there isn’t one for syntax errors. If filename is given, it is stuffed into the exception instead of the default filename provided by Python’s parser, because it always uses '<string>' when reading from a string. The output is written by the write() method.


InteractiveInterpreter.showtraceback()
Display the exception that just occurred. We remove the first stack item because it is within the interpreter object implementation. The output is written by the write() method.  Changed in version 3.5: The full chained traceback is displayed instead of just the primary traceback.


InteractiveInterpreter.write(data)
Write a string to the standard error stream (sys.stderr). Derived classes should override this to provide the appropriate output handling as needed.


codecs — Codec registry and base classes Source code: Lib/codecs.py This module defines base classes for standard Python codecs (encoders and decoders) and provides access to the internal Python codec registry, which manages the codec and error handling lookup process. Most standard codecs are text encodings, which encode text to bytes, but there are also codecs provided that encode text to text, and bytes to bytes. Custom codecs may encode and decode between arbitrary types, but some module features are restricted to use specifically with text encodings, or with codecs that encode to bytes. The module defines the following functions for encoding and decoding with any codec:
codecs.encode(obj, encoding='utf-8', errors='strict')
Encodes obj using the codec registered for encoding. Errors may be given to set the desired error handling scheme. The default error handler is 'strict' meaning that encoding errors raise ValueError (or a more codec specific subclass, such as UnicodeEncodeError). Refer to Codec Base Classes for more information on codec error handling.

codecs.decode(obj, encoding='utf-8', errors='strict')
Decodes obj using the codec registered for encoding. Errors may be given to set the desired error handling scheme. The default error handler is 'strict' meaning that decoding errors raise ValueError (or a more codec specific subclass, such as UnicodeDecodeError). Refer to Codec Base Classes for more information on codec error handling.
 The full details for each codec can also be looked up directly:
codecs.lookup(encoding)
Looks up the codec info in the Python codec registry and returns a CodecInfo object as defined below. Encodings are first looked up in the registry’s cache. If not found, the list of registered search functions is scanned. If no CodecInfo object is found, a LookupError is raised. Otherwise, the CodecInfo object is stored in the cache and returned to the caller.

class codecs.CodecInfo(encode, decode, streamreader=None, streamwriter=None, incrementalencoder=None, incrementaldecoder=None, name=None)
Codec details when looking up the codec registry. The constructor arguments are stored in attributes of the same name:
name
The name of the encoding.

encode
decode
The stateless encoding and decoding functions. These must be functions or methods which have the same interface as the encode() and decode() methods of Codec instances (see Codec Interface). The functions or methods are expected to work in a stateless mode.

incrementalencoder
incrementaldecoder
Incremental encoder and decoder classes or factory functions. These have to provide the interface defined by the base classes IncrementalEncoder and IncrementalDecoder, respectively. Incremental codecs can maintain state.

streamwriter
streamreader
Stream writer and reader classes or factory functions. These have to provide the interface defined by the base classes StreamWriter and StreamReader, respectively. Stream codecs can maintain state.

 To simplify access to the various codec components, the module provides these additional functions which use lookup() for the codec lookup:
codecs.getencoder(encoding)
Look up the codec for the given encoding and return its encoder function. Raises a LookupError in case the encoding cannot be found.

codecs.getdecoder(encoding)
Look up the codec for the given encoding and return its decoder function. Raises a LookupError in case the encoding cannot be found.

codecs.getincrementalencoder(encoding)
Look up the codec for the given encoding and return its incremental encoder class or factory function. Raises a LookupError in case the encoding cannot be found or the codec doesn’t support an incremental encoder.

codecs.getincrementaldecoder(encoding)
Look up the codec for the given encoding and return its incremental decoder class or factory function. Raises a LookupError in case the encoding cannot be found or the codec doesn’t support an incremental decoder.

codecs.getreader(encoding)
Look up the codec for the given encoding and return its StreamReader class or factory function. Raises a LookupError in case the encoding cannot be found.

codecs.getwriter(encoding)
Look up the codec for the given encoding and return its StreamWriter class or factory function. Raises a LookupError in case the encoding cannot be found.
 Custom codecs are made available by registering a suitable codec search function:
codecs.register(search_function)
Register a codec search function. Search functions are expected to take one argument, being the encoding name in all lower case letters with hyphens and spaces converted to underscores, and return a CodecInfo object. In case a search function cannot find a given encoding, it should return None.  Changed in version 3.9: Hyphens and spaces are converted to underscore.   Note Search function registration is not currently reversible, which may cause problems in some cases, such as unit testing or module reloading.
 While the builtin open() and the associated io module are the recommended approach for working with encoded text files, this module provides additional utility functions and classes that allow the use of a wider range of codecs when working with binary files:
codecs.open(filename, mode='r', encoding=None, errors='strict', buffering=-1)
Open an encoded file using the given mode and return an instance of StreamReaderWriter, providing transparent encoding/decoding. The default file mode is 'r', meaning to open the file in read mode.  Note Underlying encoded files are always opened in binary mode. No automatic conversion of '\n' is done on reading and writing. The mode argument may be any binary mode acceptable to the built-in open() function; the 'b' is automatically added.  encoding specifies the encoding which is to be used for the file. Any encoding that encodes to and decodes from bytes is allowed, and the data types supported by the file methods depend on the codec used. errors may be given to define the error handling. It defaults to 'strict' which causes a ValueError to be raised in case an encoding error occurs. buffering has the same meaning as for the built-in open() function. It defaults to -1 which means that the default buffer size will be used.

codecs.EncodedFile(file, data_encoding, file_encoding=None, errors='strict')
Return a StreamRecoder instance, a wrapped version of file which provides transparent transcoding. The original file is closed when the wrapped version is closed. Data written to the wrapped file is decoded according to the given data_encoding and then written to the original file as bytes using file_encoding. Bytes read from the original file are decoded according to file_encoding, and the result is encoded using data_encoding. If file_encoding is not given, it defaults to data_encoding. errors may be given to define the error handling. It defaults to 'strict', which causes ValueError to be raised in case an encoding error occurs.

codecs.iterencode(iterator, encoding, errors='strict', **kwargs)
Uses an incremental encoder to iteratively encode the input provided by iterator. This function is a generator. The errors argument (as well as any other keyword argument) is passed through to the incremental encoder. This function requires that the codec accept text str objects to encode. Therefore it does not support bytes-to-bytes encoders such as base64_codec.

codecs.iterdecode(iterator, encoding, errors='strict', **kwargs)
Uses an incremental decoder to iteratively decode the input provided by iterator. This function is a generator. The errors argument (as well as any other keyword argument) is passed through to the incremental decoder. This function requires that the codec accept bytes objects to decode. Therefore it does not support text-to-text encoders such as rot_13, although rot_13 may be used equivalently with iterencode().
 The module also provides the following constants which are useful for reading and writing to platform dependent files:
codecs.BOM
codecs.BOM_BE
codecs.BOM_LE
codecs.BOM_UTF8
codecs.BOM_UTF16
codecs.BOM_UTF16_BE
codecs.BOM_UTF16_LE
codecs.BOM_UTF32
codecs.BOM_UTF32_BE
codecs.BOM_UTF32_LE
These constants define various byte sequences, being Unicode byte order marks (BOMs) for several encodings. They are used in UTF-16 and UTF-32 data streams to indicate the byte order used, and in UTF-8 as a Unicode signature. BOM_UTF16 is either BOM_UTF16_BE or BOM_UTF16_LE depending on the platform’s native byte order, BOM is an alias for BOM_UTF16, BOM_LE for BOM_UTF16_LE and BOM_BE for BOM_UTF16_BE. The others represent the BOM in UTF-8 and UTF-32 encodings.
 Codec Base Classes The codecs module defines a set of base classes which define the interfaces for working with codec objects, and can also be used as the basis for custom codec implementations. Each codec has to define four interfaces to make it usable as codec in Python: stateless encoder, stateless decoder, stream reader and stream writer. The stream reader and writers typically reuse the stateless encoder/decoder to implement the file protocols. Codec authors also need to define how the codec will handle encoding and decoding errors. Error Handlers To simplify and standardize error handling, codecs may implement different error handling schemes by accepting the errors string argument. The following string values are defined and implemented by all standard Python codecs:
Value Meaning
'strict' Raise UnicodeError (or a subclass); this is the default. Implemented in strict_errors().
'ignore' Ignore the malformed data and continue without further notice. Implemented in ignore_errors().   The following error handlers are only applicable to text encodings:
Value Meaning
'replace' Replace with a suitable replacement marker; Python will use the official U+FFFD REPLACEMENT CHARACTER for the built-in codecs on decoding, and ‘?’ on encoding. Implemented in replace_errors().
'xmlcharrefreplace' Replace with the appropriate XML character reference (only for encoding). Implemented in xmlcharrefreplace_errors().
'backslashreplace' Replace with backslashed escape sequences. Implemented in backslashreplace_errors().
'namereplace' Replace with \N{...} escape sequences (only for encoding). Implemented in namereplace_errors().
'surrogateescape' On decoding, replace byte with individual surrogate code ranging from U+DC80 to U+DCFF. This code will then be turned back into the same byte when the 'surrogateescape' error handler is used when encoding the data. (See PEP 383 for more.)   In addition, the following error handler is specific to the given codecs:
Value Codecs Meaning
'surrogatepass' utf-8, utf-16, utf-32, utf-16-be, utf-16-le, utf-32-be, utf-32-le Allow encoding and decoding of surrogate codes. These codecs normally treat the presence of surrogates as an error.    New in version 3.1: The 'surrogateescape' and 'surrogatepass' error handlers.   Changed in version 3.4: The 'surrogatepass' error handlers now works with utf-16* and utf-32* codecs.   New in version 3.5: The 'namereplace' error handler.   Changed in version 3.5: The 'backslashreplace' error handlers now works with decoding and translating.  The set of allowed values can be extended by registering a new named error handler:
codecs.register_error(name, error_handler)
Register the error handling function error_handler under the name name. The error_handler argument will be called during encoding and decoding in case of an error, when name is specified as the errors parameter. For encoding, error_handler will be called with a UnicodeEncodeError instance, which contains information about the location of the error. The error handler must either raise this or a different exception, or return a tuple with a replacement for the unencodable part of the input and a position where encoding should continue. The replacement may be either str or bytes. If the replacement is bytes, the encoder will simply copy them into the output buffer. If the replacement is a string, the encoder will encode the replacement. Encoding continues on original input at the specified position. Negative position values will be treated as being relative to the end of the input string. If the resulting position is out of bound an IndexError will be raised. Decoding and translating works similarly, except UnicodeDecodeError or UnicodeTranslateError will be passed to the handler and that the replacement from the error handler will be put into the output directly.
 Previously registered error handlers (including the standard error handlers) can be looked up by name:
codecs.lookup_error(name)
Return the error handler previously registered under the name name. Raises a LookupError in case the handler cannot be found.
 The following standard error handlers are also made available as module level functions:
codecs.strict_errors(exception)
Implements the 'strict' error handling: each encoding or decoding error raises a UnicodeError.

codecs.replace_errors(exception)
Implements the 'replace' error handling (for text encodings only): substitutes '?' for encoding errors (to be encoded by the codec), and '\ufffd' (the Unicode replacement character) for decoding errors.

codecs.ignore_errors(exception)
Implements the 'ignore' error handling: malformed data is ignored and encoding or decoding is continued without further notice.

codecs.xmlcharrefreplace_errors(exception)
Implements the 'xmlcharrefreplace' error handling (for encoding with text encodings only): the unencodable character is replaced by an appropriate XML character reference.

codecs.backslashreplace_errors(exception)
Implements the 'backslashreplace' error handling (for text encodings only): malformed data is replaced by a backslashed escape sequence.

codecs.namereplace_errors(exception)
Implements the 'namereplace' error handling (for encoding with text encodings only): the unencodable character is replaced by a \N{...} escape sequence.  New in version 3.5.
 Stateless Encoding and Decoding The base Codec class defines these methods which also define the function interfaces of the stateless encoder and decoder:
Codec.encode(input[, errors])
Encodes the object input and returns a tuple (output object, length consumed). For instance, text encoding converts a string object to a bytes object using a particular character set encoding (e.g., cp1252 or iso-8859-1). The errors argument defines the error handling to apply. It defaults to 'strict' handling. The method may not store state in the Codec instance. Use StreamWriter for codecs which have to keep state in order to make encoding efficient. The encoder must be able to handle zero length input and return an empty object of the output object type in this situation.

Codec.decode(input[, errors])
Decodes the object input and returns a tuple (output object, length consumed). For instance, for a text encoding, decoding converts a bytes object encoded using a particular character set encoding to a string object. For text encodings and bytes-to-bytes codecs, input must be a bytes object or one which provides the read-only buffer interface – for example, buffer objects and memory mapped files. The errors argument defines the error handling to apply. It defaults to 'strict' handling. The method may not store state in the Codec instance. Use StreamReader for codecs which have to keep state in order to make decoding efficient. The decoder must be able to handle zero length input and return an empty object of the output object type in this situation.
 Incremental Encoding and Decoding The IncrementalEncoder and IncrementalDecoder classes provide the basic interface for incremental encoding and decoding. Encoding/decoding the input isn’t done with one call to the stateless encoder/decoder function, but with multiple calls to the encode()/decode() method of the incremental encoder/decoder. The incremental encoder/decoder keeps track of the encoding/decoding process during method calls. The joined output of calls to the encode()/decode() method is the same as if all the single inputs were joined into one, and this input was encoded/decoded with the stateless encoder/decoder. IncrementalEncoder Objects The IncrementalEncoder class is used for encoding an input in multiple steps. It defines the following methods which every incremental encoder must define in order to be compatible with the Python codec registry.
class codecs.IncrementalEncoder(errors='strict')
Constructor for an IncrementalEncoder instance. All incremental encoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry. The IncrementalEncoder may implement different error handling schemes by providing the errors keyword argument. See Error Handlers for possible values. The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the IncrementalEncoder object.
encode(object[, final])
Encodes object (taking the current state of the encoder into account) and returns the resulting encoded object. If this is the last call to encode() final must be true (the default is false).

reset()
Reset the encoder to the initial state. The output is discarded: call .encode(object, final=True), passing an empty byte or text string if necessary, to reset the encoder and to get the output.

getstate()
Return the current state of the encoder which must be an integer. The implementation should make sure that 0 is the most common state. (States that are more complicated than integers can be converted into an integer by marshaling/pickling the state and encoding the bytes of the resulting string into an integer.)

setstate(state)
Set the state of the encoder to state. state must be an encoder state returned by getstate().

 IncrementalDecoder Objects The IncrementalDecoder class is used for decoding an input in multiple steps. It defines the following methods which every incremental decoder must define in order to be compatible with the Python codec registry.
class codecs.IncrementalDecoder(errors='strict')
Constructor for an IncrementalDecoder instance. All incremental decoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry. The IncrementalDecoder may implement different error handling schemes by providing the errors keyword argument. See Error Handlers for possible values. The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the IncrementalDecoder object.
decode(object[, final])
Decodes object (taking the current state of the decoder into account) and returns the resulting decoded object. If this is the last call to decode() final must be true (the default is false). If final is true the decoder must decode the input completely and must flush all buffers. If this isn’t possible (e.g. because of incomplete byte sequences at the end of the input) it must initiate error handling just like in the stateless case (which might raise an exception).

reset()
Reset the decoder to the initial state.

getstate()
Return the current state of the decoder. This must be a tuple with two items, the first must be the buffer containing the still undecoded input. The second must be an integer and can be additional state info. (The implementation should make sure that 0 is the most common additional state info.) If this additional state info is 0 it must be possible to set the decoder to the state which has no input buffered and 0 as the additional state info, so that feeding the previously buffered input to the decoder returns it to the previous state without producing any output. (Additional state info that is more complicated than integers can be converted into an integer by marshaling/pickling the info and encoding the bytes of the resulting string into an integer.)

setstate(state)
Set the state of the decoder to state. state must be a decoder state returned by getstate().

 Stream Encoding and Decoding The StreamWriter and StreamReader classes provide generic working interfaces which can be used to implement new encoding submodules very easily. See encodings.utf_8 for an example of how this is done. StreamWriter Objects The StreamWriter class is a subclass of Codec and defines the following methods which every stream writer must define in order to be compatible with the Python codec registry.
class codecs.StreamWriter(stream, errors='strict')
Constructor for a StreamWriter instance. All stream writers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry. The stream argument must be a file-like object open for writing text or binary data, as appropriate for the specific codec. The StreamWriter may implement different error handling schemes by providing the errors keyword argument. See Error Handlers for the standard error handlers the underlying stream codec may support. The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the StreamWriter object.
write(object)
Writes the object’s contents encoded to the stream.

writelines(list)
Writes the concatenated list of strings to the stream (possibly by reusing the write() method). The standard bytes-to-bytes codecs do not support this method.

reset()
Resets the codec buffers used for keeping internal state. Calling this method should ensure that the data on the output is put into a clean state that allows appending of new fresh data without having to rescan the whole stream to recover state.

 In addition to the above methods, the StreamWriter must also inherit all other methods and attributes from the underlying stream. StreamReader Objects The StreamReader class is a subclass of Codec and defines the following methods which every stream reader must define in order to be compatible with the Python codec registry.
class codecs.StreamReader(stream, errors='strict')
Constructor for a StreamReader instance. All stream readers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry. The stream argument must be a file-like object open for reading text or binary data, as appropriate for the specific codec. The StreamReader may implement different error handling schemes by providing the errors keyword argument. See Error Handlers for the standard error handlers the underlying stream codec may support. The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the StreamReader object. The set of allowed values for the errors argument can be extended with register_error().
read([size[, chars[, firstline]]])
Decodes data from the stream and returns the resulting object. The chars argument indicates the number of decoded code points or bytes to return. The read() method will never return more data than requested, but it might return less, if there is not enough available. The size argument indicates the approximate maximum number of encoded bytes or code points to read for decoding. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. This parameter is intended to prevent having to decode huge files in one step. The firstline flag indicates that it would be sufficient to only return the first line, if there are decoding errors on later lines. The method should use a greedy read strategy meaning that it should read as much data as is allowed within the definition of the encoding and the given size, e.g. if optional encoding endings or state markers are available on the stream, these should be read too.

readline([size[, keepends]])
Read one line from the input stream and return the decoded data. size, if given, is passed as size argument to the stream’s read() method. If keepends is false line-endings will be stripped from the lines returned.

readlines([sizehint[, keepends]])
Read all lines available on the input stream and return them as a list of lines. Line-endings are implemented using the codec’s decode() method and are included in the list entries if keepends is true. sizehint, if given, is passed as the size argument to the stream’s read() method.

reset()
Resets the codec buffers used for keeping internal state. Note that no stream repositioning should take place. This method is primarily intended to be able to recover from decoding errors.

 In addition to the above methods, the StreamReader must also inherit all other methods and attributes from the underlying stream. StreamReaderWriter Objects The StreamReaderWriter is a convenience class that allows wrapping streams which work in both read and write modes. The design is such that one can use the factory functions returned by the lookup() function to construct the instance.
class codecs.StreamReaderWriter(stream, Reader, Writer, errors='strict')
Creates a StreamReaderWriter instance. stream must be a file-like object. Reader and Writer must be factory functions or classes providing the StreamReader and StreamWriter interface resp. Error handling is done in the same way as defined for the stream readers and writers.
 StreamReaderWriter instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream. StreamRecoder Objects The StreamRecoder translates data from one encoding to another, which is sometimes useful when dealing with different encoding environments. The design is such that one can use the factory functions returned by the lookup() function to construct the instance.
class codecs.StreamRecoder(stream, encode, decode, Reader, Writer, errors='strict')
Creates a StreamRecoder instance which implements a two-way conversion: encode and decode work on the frontend — the data visible to code calling read() and write(), while Reader and Writer work on the backend — the data in stream. You can use these objects to do transparent transcodings, e.g., from Latin-1 to UTF-8 and back. The stream argument must be a file-like object. The encode and decode arguments must adhere to the Codec interface. Reader and Writer must be factory functions or classes providing objects of the StreamReader and StreamWriter interface respectively. Error handling is done in the same way as defined for the stream readers and writers.
 StreamRecoder instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream. Encodings and Unicode Strings are stored internally as sequences of code points in range 0x0–0x10FFFF. (See PEP 393 for more details about the implementation.) Once a string object is used outside of CPU and memory, endianness and how these arrays are stored as bytes become an issue. As with other codecs, serialising a string into a sequence of bytes is known as encoding, and recreating the string from the sequence of bytes is known as decoding. There are a variety of different text serialisation codecs, which are collectivity referred to as text encodings. The simplest text encoding (called 'latin-1' or 'iso-8859-1') maps the code points 0–255 to the bytes 0x0–0xff, which means that a string object that contains code points above U+00FF can’t be encoded with this codec. Doing so will raise a UnicodeEncodeError that looks like the following (although the details of the error message may differ): UnicodeEncodeError: 'latin-1' codec can't encode character '\u1234' in
position 3: ordinal not in range(256). There’s another group of encodings (the so called charmap encodings) that choose a different subset of all Unicode code points and how these code points are mapped to the bytes 0x0–0xff. To see how this is done simply open e.g. encodings/cp1252.py (which is an encoding that is used primarily on Windows). There’s a string constant with 256 characters that shows you which character is mapped to which byte value. All of these encodings can only encode 256 of the 1114112 code points defined in Unicode. A simple and straightforward way that can store each Unicode code point, is to store each code point as four consecutive bytes. There are two possibilities: store the bytes in big endian or in little endian order. These two encodings are called UTF-32-BE and UTF-32-LE respectively. Their disadvantage is that if e.g. you use UTF-32-BE on a little endian machine you will always have to swap bytes on encoding and decoding. UTF-32 avoids this problem: bytes will always be in natural endianness. When these bytes are read by a CPU with a different endianness, then bytes have to be swapped though. To be able to detect the endianness of a UTF-16 or UTF-32 byte sequence, there’s the so called BOM (“Byte Order Mark”). This is the Unicode character U+FEFF. This character can be prepended to every UTF-16 or UTF-32 byte sequence. The byte swapped version of this character (0xFFFE) is an illegal character that may not appear in a Unicode text. So when the first character in an UTF-16 or UTF-32 byte sequence appears to be a U+FFFE the bytes have to be swapped on decoding. Unfortunately the character U+FEFF had a second purpose as a ZERO WIDTH NO-BREAK SPACE: a character that has no width and doesn’t allow a word to be split. It can e.g. be used to give hints to a ligature algorithm. With Unicode 4.0 using U+FEFF as a ZERO WIDTH NO-BREAK SPACE has been deprecated (with U+2060 (WORD JOINER) assuming this role). Nevertheless Unicode software still must be able to handle U+FEFF in both roles: as a BOM it’s a device to determine the storage layout of the encoded bytes, and vanishes once the byte sequence has been decoded into a string; as a ZERO WIDTH
NO-BREAK SPACE it’s a normal character that will be decoded like any other. There’s another encoding that is able to encoding the full range of Unicode characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two parts: marker bits (the most significant bits) and payload bits. The marker bits are a sequence of zero to four 1 bits followed by a 0 bit. Unicode characters are encoded like this (with x being payload bits, which when concatenated give the Unicode character):
Range Encoding
U-00000000 … U-0000007F 0xxxxxxx
U-00000080 … U-000007FF 110xxxxx 10xxxxxx
U-00000800 … U-0000FFFF 1110xxxx 10xxxxxx 10xxxxxx
U-00010000 … U-0010FFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx   The least significant bit of the Unicode character is the rightmost x bit. As UTF-8 is an 8-bit encoding no BOM is required and any U+FEFF character in the decoded string (even if it’s the first character) is treated as a ZERO
WIDTH NO-BREAK SPACE. Without external information it’s impossible to reliably determine which encoding was used for encoding a string. Each charmap encoding can decode any random byte sequence. However that’s not possible with UTF-8, as UTF-8 byte sequences have a structure that doesn’t allow arbitrary byte sequences. To increase the reliability with which a UTF-8 encoding can be detected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls "utf-8-sig") for its Notepad program: Before any of the Unicode characters is written to the file, a UTF-8 encoded BOM (which looks like this as a byte sequence: 0xef, 0xbb, 0xbf) is written. As it’s rather improbable that any charmap encoded file starts with these byte values (which would e.g. map to in iso-8859-1), this increases the probability that a utf-8-sig encoding can be correctly guessed from the byte sequence. So here the BOM is not used to be able to determine the byte order used for generating the byte sequence, but as a signature that helps in guessing the encoding. On encoding the utf-8-sig codec will write 0xef, 0xbb, 0xbf as the first three bytes to the file. On decoding utf-8-sig will skip those three bytes if they appear as the first three bytes in the file. In UTF-8, the use of the BOM is discouraged and should generally be avoided. Standard Encodings Python comes with a number of codecs built-in, either implemented as C functions or with dictionaries as mapping tables. The following table lists the codecs by name, together with a few common aliases, and the languages for which the encoding is likely used. Neither the list of aliases nor the list of languages is meant to be exhaustive. Notice that spelling alternatives that only differ in case or use a hyphen instead of an underscore are also valid aliases; therefore, e.g. 'utf-8' is a valid alias for the 'utf_8' codec.  CPython implementation detail: Some common encodings can bypass the codecs lookup machinery to improve performance. These optimization opportunities are only recognized by CPython for a limited set of (case insensitive) aliases: utf-8, utf8, latin-1, latin1, iso-8859-1, iso8859-1, mbcs (Windows only), ascii, us-ascii, utf-16, utf16, utf-32, utf32, and the same using underscores instead of dashes. Using alternative aliases for these encodings may result in slower execution.  Changed in version 3.6: Optimization opportunity recognized for us-ascii.   Many of the character sets support the same languages. They vary in individual characters (e.g. whether the EURO SIGN is supported or not), and in the assignment of characters to code positions. For the European languages in particular, the following variants typically exist:  an ISO 8859 codeset a Microsoft Windows code page, which is typically derived from an 8859 codeset, but replaces control characters with additional graphic characters an IBM EBCDIC code page an IBM PC code page, which is ASCII compatible
Codec Aliases Languages
ascii 646, us-ascii English
big5 big5-tw, csbig5 Traditional Chinese
big5hkscs big5-hkscs, hkscs Traditional Chinese
cp037 IBM037, IBM039 English
cp273 273, IBM273, csIBM273
German  New in version 3.4.
cp424 EBCDIC-CP-HE, IBM424 Hebrew
cp437 437, IBM437 English
cp500 EBCDIC-CP-BE, EBCDIC-CP-CH, IBM500 Western Europe
cp720  Arabic
cp737  Greek
cp775 IBM775 Baltic languages
cp850 850, IBM850 Western Europe
cp852 852, IBM852 Central and Eastern Europe
cp855 855, IBM855 Bulgarian, Byelorussian, Macedonian, Russian, Serbian
cp856  Hebrew
cp857 857, IBM857 Turkish
cp858 858, IBM858 Western Europe
cp860 860, IBM860 Portuguese
cp861 861, CP-IS, IBM861 Icelandic
cp862 862, IBM862 Hebrew
cp863 863, IBM863 Canadian
cp864 IBM864 Arabic
cp865 865, IBM865 Danish, Norwegian
cp866 866, IBM866 Russian
cp869 869, CP-GR, IBM869 Greek
cp874  Thai
cp875  Greek
cp932 932, ms932, mskanji, ms-kanji Japanese
cp949 949, ms949, uhc Korean
cp950 950, ms950 Traditional Chinese
cp1006  Urdu
cp1026 ibm1026 Turkish
cp1125 1125, ibm1125, cp866u, ruscii
Ukrainian  New in version 3.4.
cp1140 ibm1140 Western Europe
cp1250 windows-1250 Central and Eastern Europe
cp1251 windows-1251 Bulgarian, Byelorussian, Macedonian, Russian, Serbian
cp1252 windows-1252 Western Europe
cp1253 windows-1253 Greek
cp1254 windows-1254 Turkish
cp1255 windows-1255 Hebrew
cp1256 windows-1256 Arabic
cp1257 windows-1257 Baltic languages
cp1258 windows-1258 Vietnamese
euc_jp eucjp, ujis, u-jis Japanese
euc_jis_2004 jisx0213, eucjis2004 Japanese
euc_jisx0213 eucjisx0213 Japanese
euc_kr euckr, korean, ksc5601, ks_c-5601, ks_c-5601-1987, ksx1001, ks_x-1001 Korean
gb2312 chinese, csiso58gb231280, euc-cn, euccn, eucgb2312-cn, gb2312-1980, gb2312-80, iso-ir-58 Simplified Chinese
gbk 936, cp936, ms936 Unified Chinese
gb18030 gb18030-2000 Unified Chinese
hz hzgb, hz-gb, hz-gb-2312 Simplified Chinese
iso2022_jp csiso2022jp, iso2022jp, iso-2022-jp Japanese
iso2022_jp_1 iso2022jp-1, iso-2022-jp-1 Japanese
iso2022_jp_2 iso2022jp-2, iso-2022-jp-2 Japanese, Korean, Simplified Chinese, Western Europe, Greek
iso2022_jp_2004 iso2022jp-2004, iso-2022-jp-2004 Japanese
iso2022_jp_3 iso2022jp-3, iso-2022-jp-3 Japanese
iso2022_jp_ext iso2022jp-ext, iso-2022-jp-ext Japanese
iso2022_kr csiso2022kr, iso2022kr, iso-2022-kr Korean
latin_1 iso-8859-1, iso8859-1, 8859, cp819, latin, latin1, L1 Western Europe
iso8859_2 iso-8859-2, latin2, L2 Central and Eastern Europe
iso8859_3 iso-8859-3, latin3, L3 Esperanto, Maltese
iso8859_4 iso-8859-4, latin4, L4 Baltic languages
iso8859_5 iso-8859-5, cyrillic Bulgarian, Byelorussian, Macedonian, Russian, Serbian
iso8859_6 iso-8859-6, arabic Arabic
iso8859_7 iso-8859-7, greek, greek8 Greek
iso8859_8 iso-8859-8, hebrew Hebrew
iso8859_9 iso-8859-9, latin5, L5 Turkish
iso8859_10 iso-8859-10, latin6, L6 Nordic languages
iso8859_11 iso-8859-11, thai Thai languages
iso8859_13 iso-8859-13, latin7, L7 Baltic languages
iso8859_14 iso-8859-14, latin8, L8 Celtic languages
iso8859_15 iso-8859-15, latin9, L9 Western Europe
iso8859_16 iso-8859-16, latin10, L10 South-Eastern Europe
johab cp1361, ms1361 Korean
koi8_r  Russian
koi8_t
Tajik  New in version 3.5.
koi8_u  Ukrainian
kz1048 kz_1048, strk1048_2002, rk1048
Kazakh  New in version 3.5.
mac_cyrillic maccyrillic Bulgarian, Byelorussian, Macedonian, Russian, Serbian
mac_greek macgreek Greek
mac_iceland maciceland Icelandic
mac_latin2 maclatin2, maccentraleurope, mac_centeuro Central and Eastern Europe
mac_roman macroman, macintosh Western Europe
mac_turkish macturkish Turkish
ptcp154 csptcp154, pt154, cp154, cyrillic-asian Kazakh
shift_jis csshiftjis, shiftjis, sjis, s_jis Japanese
shift_jis_2004 shiftjis2004, sjis_2004, sjis2004 Japanese
shift_jisx0213 shiftjisx0213, sjisx0213, s_jisx0213 Japanese
utf_32 U32, utf32 all languages
utf_32_be UTF-32BE all languages
utf_32_le UTF-32LE all languages
utf_16 U16, utf16 all languages
utf_16_be UTF-16BE all languages
utf_16_le UTF-16LE all languages
utf_7 U7, unicode-1-1-utf-7 all languages
utf_8 U8, UTF, utf8, cp65001 all languages
utf_8_sig  all languages    Changed in version 3.4: The utf-16* and utf-32* encoders no longer allow surrogate code points (U+D800–U+DFFF) to be encoded. The utf-32* decoders no longer decode byte sequences that correspond to surrogate code points.   Changed in version 3.8: cp65001 is now an alias to utf_8.  Python Specific Encodings A number of predefined codecs are specific to Python, so their codec names have no meaning outside Python. These are listed in the tables below based on the expected input and output types (note that while text encodings are the most common use case for codecs, the underlying codec infrastructure supports arbitrary data transforms rather than just text encodings). For asymmetric codecs, the stated meaning describes the encoding direction. Text Encodings The following codecs provide str to bytes encoding and bytes-like object to str decoding, similar to the Unicode text encodings.
Codec Aliases Meaning
idna  Implement RFC 3490, see also encodings.idna. Only errors='strict' is supported.
mbcs ansi, dbcs Windows only: Encode the operand according to the ANSI codepage (CP_ACP).
oem
Windows only: Encode the operand according to the OEM codepage (CP_OEMCP).  New in version 3.6.
palmos  Encoding of PalmOS 3.5.
punycode  Implement RFC 3492. Stateful codecs are not supported.
raw_unicode_escape  Latin-1 encoding with \uXXXX and \UXXXXXXXX for other code points. Existing backslashes are not escaped in any way. It is used in the Python pickle protocol.
undefined  Raise an exception for all conversions, even empty strings. The error handler is ignored.
unicode_escape  Encoding suitable as the contents of a Unicode literal in ASCII-encoded Python source code, except that quotes are not escaped. Decode from Latin-1 source code. Beware that Python source code actually uses UTF-8 by default.    Changed in version 3.8: “unicode_internal” codec is removed.  Binary Transforms The following codecs provide binary transforms: bytes-like object to bytes mappings. They are not supported by bytes.decode() (which only produces str output).
Codec Aliases Meaning Encoder / decoder
base64_codec 1 base64, base_64
Convert the operand to multiline MIME base64 (the result always includes a trailing '\n').  Changed in version 3.4: accepts any bytes-like object as input for encoding and decoding   base64.encodebytes() / base64.decodebytes()
bz2_codec bz2 Compress the operand using bz2. bz2.compress() / bz2.decompress()
hex_codec hex Convert the operand to hexadecimal representation, with two digits per byte. binascii.b2a_hex() / binascii.a2b_hex()
quopri_codec quopri, quotedprintable, quoted_printable Convert the operand to MIME quoted printable. quopri.encode() with quotetabs=True / quopri.decode()
uu_codec uu Convert the operand using uuencode. uu.encode() / uu.decode()
zlib_codec zip, zlib Compress the operand using gzip. zlib.compress() / zlib.decompress()
1
In addition to bytes-like objects, 'base64_codec' also accepts ASCII-only instances of str for decoding    New in version 3.2: Restoration of the binary transforms.   Changed in version 3.4: Restoration of the aliases for the binary transforms.  Text Transforms The following codec provides a text transform: a str to str mapping. It is not supported by str.encode() (which only produces bytes output).
Codec Aliases Meaning
rot_13 rot13 Return the Caesar-cypher encryption of the operand.    New in version 3.2: Restoration of the rot_13 text transform.   Changed in version 3.4: Restoration of the rot13 alias.  encodings.idna — Internationalized Domain Names in Applications This module implements RFC 3490 (Internationalized Domain Names in Applications) and RFC 3492 (Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)). It builds upon the punycode encoding and stringprep. If you need the IDNA 2008 standard from RFC 5891 and RFC 5895, use the third-party idna module <https://pypi.org/project/idna/>_. These RFCs together define a protocol to support non-ASCII characters in domain names. A domain name containing non-ASCII characters (such as www.Alliancefrançaise.nu) is converted into an ASCII-compatible encoding (ACE, such as www.xn--alliancefranaise-npb.nu). The ACE form of the domain name is then used in all places where arbitrary characters are not allowed by the protocol, such as DNS queries, HTTP Host fields, and so on. This conversion is carried out in the application; if possible invisible to the user: The application should transparently convert Unicode domain labels to IDNA on the wire, and convert back ACE labels to Unicode before presenting them to the user. Python supports this conversion in several ways: the idna codec performs conversion between Unicode and ACE, separating an input string into labels based on the separator characters defined in section 3.1 of RFC 3490 and converting each label to ACE as required, and conversely separating an input byte string into labels based on the . separator and converting any ACE labels found into unicode. Furthermore, the socket module transparently converts Unicode host names to ACE, so that applications need not be concerned about converting host names themselves when they pass them to the socket module. On top of that, modules that have host names as function parameters, such as http.client and ftplib, accept Unicode host names (http.client then also transparently sends an IDNA hostname in the Host field if it sends that field at all). When receiving host names from the wire (such as in reverse name lookup), no automatic conversion to Unicode is performed: applications wishing to present such host names to the user should decode them to Unicode. The module encodings.idna also implements the nameprep procedure, which performs certain normalizations on host names, to achieve case-insensitivity of international domain names, and to unify similar characters. The nameprep functions can be used directly if desired.
encodings.idna.nameprep(label)
Return the nameprepped version of label. The implementation currently assumes query strings, so AllowUnassigned is true.

encodings.idna.ToASCII(label)
Convert a label to ASCII, as specified in RFC 3490. UseSTD3ASCIIRules is assumed to be false.

encodings.idna.ToUnicode(label)
Convert a label to Unicode, as specified in RFC 3490.
 encodings.mbcs — Windows ANSI codepage This module implements the ANSI codepage (CP_ACP). Availability: Windows only.  Changed in version 3.3: Support any error handler.   Changed in version 3.2: Before 3.2, the errors argument was ignored; 'replace' was always used to encode, and 'ignore' to decode.  encodings.utf_8_sig — UTF-8 codec with BOM signature This module implements a variant of the UTF-8 codec. On encoding, a UTF-8 encoded BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this is only done once (on the first write to the byte stream). On decoding, an optional UTF-8 encoded BOM at the start of the data will be skipped.


codecs.backslashreplace_errors(exception)
Implements the 'backslashreplace' error handling (for text encodings only): malformed data is replaced by a backslashed escape sequence.


codecs.BOM
codecs.BOM_BE
codecs.BOM_LE
codecs.BOM_UTF8
codecs.BOM_UTF16
codecs.BOM_UTF16_BE
codecs.BOM_UTF16_LE
codecs.BOM_UTF32
codecs.BOM_UTF32_BE
codecs.BOM_UTF32_LE
These constants define various byte sequences, being Unicode byte order marks (BOMs) for several encodings. They are used in UTF-16 and UTF-32 data streams to indicate the byte order used, and in UTF-8 as a Unicode signature. BOM_UTF16 is either BOM_UTF16_BE or BOM_UTF16_LE depending on the platform’s native byte order, BOM is an alias for BOM_UTF16, BOM_LE for BOM_UTF16_LE and BOM_BE for BOM_UTF16_BE. The others represent the BOM in UTF-8 and UTF-32 encodings.


Codec.decode(input[, errors])
Decodes the object input and returns a tuple (output object, length consumed). For instance, for a text encoding, decoding converts a bytes object encoded using a particular character set encoding to a string object. For text encodings and bytes-to-bytes codecs, input must be a bytes object or one which provides the read-only buffer interface – for example, buffer objects and memory mapped files. The errors argument defines the error handling to apply. It defaults to 'strict' handling. The method may not store state in the Codec instance. Use StreamReader for codecs which have to keep state in order to make decoding efficient. The decoder must be able to handle zero length input and return an empty object of the output object type in this situation.