python_doc_md/Intermediate/library/binascii.md

!binascii{.interpreted-text role="mod"} --- Convert between binary and ASCII

::: {.module synopsis="Tools for converting between binary and various ASCII-encoded binary representations."} binascii :::

::: index pair: module; base64 :::

---

The !binascii{.interpreted-text role="mod"} module contains a number of methods to convert between binary and various ASCII-encoded binary representations. Normally, you will not use these functions directly but use wrapper modules like base64{.interpreted-text role="mod"} instead. The !binascii{.interpreted-text role="mod"} module contains low-level functions written in C for greater speed that are used by the higher-level modules.

::::: note ::: title Note :::

a2b_* functions accept Unicode strings containing only ASCII characters. Other functions only accept bytes-like objects <bytes-like object>{.interpreted-text role="term"} (such as bytes{.interpreted-text role="class"}, bytearray{.interpreted-text role="class"} and other objects that support the buffer protocol).

::: versionchanged 3.3 ASCII-only unicode strings are now accepted by the a2b_* functions. ::: :::::

The !binascii{.interpreted-text role="mod"} module defines the following functions:

::: function a2b_uu(string)

Convert a single line of uuencoded data back to binary and return the binary data. Lines normally contain 45 (binary) bytes, except for the last line. Line data may be followed by whitespace. :::

:::: function b2a_uu(data, *, backtick=False)

Convert binary data to a line of ASCII characters, the return value is the converted line, including a newline char. The length of data should be at most 45. If backtick is true, zeros are represented by '`' instead of spaces.

::: versionchanged 3.7 Added the backtick parameter. ::: ::::

::::: function a2b_base64(string, /, , strict_mode=False) a2b_base64(string, /,, strict_mode=True, ignorechars)

Convert a block of base64 data back to binary and return the binary data. More than one line may be passed at a time.

If ignorechars is specified, it should be a bytes-like object{.interpreted-text role="term"} containing characters to ignore from the input when strict_mode is true. If ignorechars contains the pad character '=', the pad characters presented before the end of the encoded data and the excess pad characters will be ignored. The default value of strict_mode is True if ignorechars is specified, False otherwise.

If strict_mode is true, only valid base64 data will be converted. Invalid base64 data will raise binascii.Error{.interpreted-text role="exc"}.

Valid base64:

• Conforms to 4648{.interpreted-text role="rfc"}.
• Contains only characters from the base64 alphabet.
• Contains no excess data after padding (including excess padding, newlines, etc.).
• Does not start with a padding.

::: versionchanged 3.11 Added the strict_mode parameter. :::

::: versionchanged 3.15 Added the ignorechars parameter. ::: :::::

::::: function b2a_base64(data, *, wrapcol=0, newline=True)

Convert binary data to a line(s) of ASCII characters in base64 coding, as specified in 4648{.interpreted-text role="rfc"}.

If wrapcol is non-zero, insert a newline (b'\n') character after at most every wrapcol characters. If wrapcol is zero (default), do not insert any newlines.

If newline is true (default), a newline character will be added at the end of the output.

::: versionchanged 3.6 Added the newline parameter. :::

::: versionchanged 3.15 Added the wrapcol parameter. ::: :::::

:::: function a2b_ascii85(string, /, *, foldspaces=False, adobe=False, ignorechars=b"")

Convert Ascii85 data back to binary and return the binary data.

Valid Ascii85 data contains characters from the Ascii85 alphabet in groups of five (except for the final group, which may have from two to five characters). Each group encodes 32 bits of binary data in the range from 0 to 2 ** 32 - 1, inclusive. The special character z is accepted as a short form of the group !!!!!, which encodes four consecutive null bytes.

foldspaces is a flag that specifies whether the 'y' short sequence should be accepted as shorthand for 4 consecutive spaces (ASCII 0x20). This feature is not supported by the "standard" Ascii85 encoding.

adobe controls whether the input sequence is in Adobe Ascii85 format (i.e. is framed with <~ and ~>).

ignorechars should be a bytes-like object{.interpreted-text role="term"} containing characters to ignore from the input. This should only contain whitespace characters.

Invalid Ascii85 data will raise binascii.Error{.interpreted-text role="exc"}.

::: versionadded 3.15 ::: ::::

:::: function b2a_ascii85(data, /, *, foldspaces=False, wrapcol=0, pad=False, adobe=False)

Convert binary data to a formatted sequence of ASCII characters in Ascii85 coding. The return value is the converted data.

foldspaces is an optional flag that uses the special short sequence 'y' instead of 4 consecutive spaces (ASCII 0x20) as supported by 'btoa'. This feature is not supported by the "standard" Ascii85 encoding.

If wrapcol is non-zero, insert a newline (b'\n') character after at most every wrapcol characters. If wrapcol is zero (default), do not insert any newlines.

If pad is true, the input is padded with b'\0' so its length is a multiple of 4 bytes before encoding. Note that the btoa implementation always pads.

adobe controls whether the encoded byte sequence is framed with <~ and ~>, which is used by the Adobe implementation.

::: versionadded 3.15 ::: ::::

:::: function a2b_base85(string, /)

Convert Base85 data back to binary and return the binary data. More than one line may be passed at a time.

Valid Base85 data contains characters from the Base85 alphabet in groups of five (except for the final group, which may have from two to five characters). Each group encodes 32 bits of binary data in the range from 0 to 2 ** 32 - 1, inclusive.

Invalid Base85 data will raise binascii.Error{.interpreted-text role="exc"}.

::: versionadded 3.15 ::: ::::

:::: function b2a_base85(data, /, *, pad=False)

Convert binary data to a line of ASCII characters in Base85 coding. The return value is the converted line.

If pad is true, the input is padded with b'\0' so its length is a multiple of 4 bytes before encoding.

::: versionadded 3.15 ::: ::::

:::: function a2b_z85(string, /)

Convert Z85 data back to binary and return the binary data. More than one line may be passed at a time.

Valid Z85 data contains characters from the Z85 alphabet in groups of five (except for the final group, which may have from two to five characters). Each group encodes 32 bits of binary data in the range from 0 to 2 ** 32 - 1, inclusive.

See Z85 specification for more information.

Invalid Z85 data will raise binascii.Error{.interpreted-text role="exc"}.

::: versionadded 3.15 ::: ::::

:::: function b2a_z85(data, /, *, pad=False)

Convert binary data to a line of ASCII characters in Z85 coding. The return value is the converted line.

If pad is true, the input is padded with b'\0' so its length is a multiple of 4 bytes before encoding.

See Z85 specification for more information.

::: versionadded 3.15 ::: ::::

::: function a2b_qp(data, header=False)

Convert a block of quoted-printable data back to binary and return the binary data. More than one line may be passed at a time. If the optional argument header is present and true, underscores will be decoded as spaces. :::

::: function b2a_qp(data, quotetabs=False, istext=True, header=False)

Convert binary data to a line(s) of ASCII characters in quoted-printable encoding. The return value is the converted line(s). If the optional argument quotetabs is present and true, all tabs and spaces will be encoded. If the optional argument istext is present and true, newlines are not encoded but trailing whitespace will be encoded. If the optional argument header is present and true, spaces will be encoded as underscores per 1522{.interpreted-text role="rfc"}. If the optional argument header is present and false, newline characters will be encoded as well; otherwise linefeed conversion might corrupt the binary data stream. :::

::: function crc_hqx(data, value)

Compute a 16-bit CRC value of data, starting with value as the initial CRC, and return the result. This uses the CRC-CCITT polynomial x^16^ + x^12^ + x^5^ + 1, often represented as 0x1021. This CRC is used in the binhex4 format. :::

:::: function crc32(data[, value])

Compute CRC-32, the unsigned 32-bit checksum of data, starting with an initial CRC of value. The default initial CRC is zero. The algorithm is consistent with the ZIP file checksum. Since the algorithm is designed for use as a checksum algorithm, it is not suitable for use as a general hash algorithm. Use as follows:

print(binascii.crc32(b"hello world"))
# Or, in two pieces:
crc = binascii.crc32(b"hello")
crc = binascii.crc32(b" world", crc)
print('crc32 = {:#010x}'.format(crc))

::: versionchanged 3.0 The result is always unsigned. ::: ::::

:::: function b2a_hex(data[, sep[, bytes_per_sep=1]]) hexlify(data[, sep[, bytes_per_sep=1]])

Return the hexadecimal representation of the binary data. Every byte of data is converted into the corresponding 2-digit hex representation. The returned bytes object is therefore twice as long as the length of data.

Similar functionality (but returning a text string) is also conveniently accessible using the bytes.hex{.interpreted-text role="meth"} method.

If sep is specified, it must be a single character str or bytes object. It will be inserted in the output after every bytes_per_sep input bytes. Separator placement is counted from the right end of the output by default, if you wish to count from the left, supply a negative bytes_per_sep value.

>>> import binascii >>> binascii.b2a_hex(b'xb9x01xef') b'b901ef' >>> binascii.hexlify(b'xb9x01xef', '-') b'b9-01-ef' >>> binascii.b2a_hex(b'xb9x01xef', b'_', 2) b'b9_01ef' >>> binascii.b2a_hex(b'xb9x01xef', b' ', -2) b'b901 ef'

::: versionchanged 3.8 The sep and bytes_per_sep parameters were added. ::: ::::

::: function a2b_hex(hexstr) unhexlify(hexstr)

Return the binary data represented by the hexadecimal string hexstr. This function is the inverse of b2a_hex{.interpreted-text role="func"}. hexstr must contain an even number of hexadecimal digits (which can be upper or lower case), otherwise an Error{.interpreted-text role="exc"} exception is raised.

Similar functionality (accepting only text string arguments, but more liberal towards whitespace) is also accessible using the bytes.fromhex{.interpreted-text role="meth"} class method. :::

::: exception Error

Exception raised on errors. These are usually programming errors. :::

::: exception Incomplete

Exception raised on incomplete data. These are usually not programming errors, but may be handled by reading a little more data and trying again. :::

::: seealso

Module base64{.interpreted-text role="mod"}

: Support for RFC compliant base64-style encoding in base 16, 32, 64, and 85.

Module quopri{.interpreted-text role="mod"}

: Support for quoted-printable encoding used in MIME email messages. :::