1:mod:`binascii` --- Convert between binary and ASCII
2====================================================
3
4.. module:: binascii
5   :synopsis: Tools for converting between binary and various ASCII-encoded binary
6              representations.
7
8.. index::
9   pair: module; uu
10   pair: module; base64
11
12--------------
13
14The :mod:`binascii` module contains a number of methods to convert between
15binary and various ASCII-encoded binary representations. Normally, you will not
16use these functions directly but use wrapper modules like :mod:`uu` or
17:mod:`base64` instead. The :mod:`binascii` module contains
18low-level functions written in C for greater speed that are used by the
19higher-level modules.
20
21.. note::
22
23   ``a2b_*`` functions accept Unicode strings containing only ASCII characters.
24   Other functions only accept :term:`bytes-like objects <bytes-like object>` (such as
25   :class:`bytes`, :class:`bytearray` and other objects that support the buffer
26   protocol).
27
28   .. versionchanged:: 3.3
29      ASCII-only unicode strings are now accepted by the ``a2b_*`` functions.
30
31
32The :mod:`binascii` module defines the following functions:
33
34
35.. function:: a2b_uu(string)
36
37   Convert a single line of uuencoded data back to binary and return the binary
38   data. Lines normally contain 45 (binary) bytes, except for the last line. Line
39   data may be followed by whitespace.
40
41
42.. function:: b2a_uu(data, *, backtick=False)
43
44   Convert binary data to a line of ASCII characters, the return value is the
45   converted line, including a newline char. The length of *data* should be at most
46   45. If *backtick* is true, zeros are represented by ``'`'`` instead of spaces.
47
48   .. versionchanged:: 3.7
49      Added the *backtick* parameter.
50
51
52.. function:: a2b_base64(string, /, *, strict_mode=False)
53
54   Convert a block of base64 data back to binary and return the binary data. More
55   than one line may be passed at a time.
56
57   If *strict_mode* is true, only valid base64 data will be converted. Invalid base64
58   data will raise :exc:`binascii.Error`.
59
60   Valid base64:
61      * Conforms to :rfc:`3548`.
62      * Contains only characters from the base64 alphabet.
63      * Contains no excess data after padding (including excess padding, newlines, etc.).
64      * Does not start with a padding.
65
66   .. versionchanged:: 3.11
67      Added the *strict_mode* parameter.
68
69
70.. function:: b2a_base64(data, *, newline=True)
71
72   Convert binary data to a line of ASCII characters in base64 coding. The return
73   value is the converted line, including a newline char if *newline* is
74   true.  The output of this function conforms to :rfc:`3548`.
75
76   .. versionchanged:: 3.6
77      Added the *newline* parameter.
78
79
80.. function:: a2b_qp(data, header=False)
81
82   Convert a block of quoted-printable data back to binary and return the binary
83   data. More than one line may be passed at a time. If the optional argument
84   *header* is present and true, underscores will be decoded as spaces.
85
86
87.. function:: b2a_qp(data, quotetabs=False, istext=True, header=False)
88
89   Convert binary data to a line(s) of ASCII characters in quoted-printable
90   encoding.  The return value is the converted line(s). If the optional argument
91   *quotetabs* is present and true, all tabs and spaces will be encoded.   If the
92   optional argument *istext* is present and true, newlines are not encoded but
93   trailing whitespace will be encoded. If the optional argument *header* is
94   present and true, spaces will be encoded as underscores per :rfc:`1522`. If the
95   optional argument *header* is present and false, newline characters will be
96   encoded as well; otherwise linefeed conversion might corrupt the binary data
97   stream.
98
99
100.. function:: crc_hqx(data, value)
101
102   Compute a 16-bit CRC value of *data*, starting with *value* as the
103   initial CRC, and return the result.  This uses the CRC-CCITT polynomial
104   *x*:sup:`16` + *x*:sup:`12` + *x*:sup:`5` + 1, often represented as
105   0x1021.  This CRC is used in the binhex4 format.
106
107
108.. function:: crc32(data[, value])
109
110   Compute CRC-32, the unsigned 32-bit checksum of *data*, starting with an
111   initial CRC of *value*.  The default initial CRC is zero.  The algorithm
112   is consistent with the ZIP file checksum.  Since the algorithm is designed for
113   use as a checksum algorithm, it is not suitable for use as a general hash
114   algorithm.  Use as follows::
115
116      print(binascii.crc32(b"hello world"))
117      # Or, in two pieces:
118      crc = binascii.crc32(b"hello")
119      crc = binascii.crc32(b" world", crc)
120      print('crc32 = {:#010x}'.format(crc))
121
122   .. versionchanged:: 3.0
123      The result is always unsigned.
124
125.. function:: b2a_hex(data[, sep[, bytes_per_sep=1]])
126              hexlify(data[, sep[, bytes_per_sep=1]])
127
128   Return the hexadecimal representation of the binary *data*.  Every byte of
129   *data* is converted into the corresponding 2-digit hex representation.  The
130   returned bytes object is therefore twice as long as the length of *data*.
131
132   Similar functionality (but returning a text string) is also conveniently
133   accessible using the :meth:`bytes.hex` method.
134
135   If *sep* is specified, it must be a single character str or bytes object.
136   It will be inserted in the output after every *bytes_per_sep* input bytes.
137   Separator placement is counted from the right end of the output by default,
138   if you wish to count from the left, supply a negative *bytes_per_sep* value.
139
140      >>> import binascii
141      >>> binascii.b2a_hex(b'\xb9\x01\xef')
142      b'b901ef'
143      >>> binascii.hexlify(b'\xb9\x01\xef', '-')
144      b'b9-01-ef'
145      >>> binascii.b2a_hex(b'\xb9\x01\xef', b'_', 2)
146      b'b9_01ef'
147      >>> binascii.b2a_hex(b'\xb9\x01\xef', b' ', -2)
148      b'b901 ef'
149
150   .. versionchanged:: 3.8
151      The *sep* and *bytes_per_sep* parameters were added.
152
153.. function:: a2b_hex(hexstr)
154              unhexlify(hexstr)
155
156   Return the binary data represented by the hexadecimal string *hexstr*.  This
157   function is the inverse of :func:`b2a_hex`. *hexstr* must contain an even number
158   of hexadecimal digits (which can be upper or lower case), otherwise an
159   :exc:`Error` exception is raised.
160
161   Similar functionality (accepting only text string arguments, but more
162   liberal towards whitespace) is also accessible using the
163   :meth:`bytes.fromhex` class method.
164
165.. exception:: Error
166
167   Exception raised on errors. These are usually programming errors.
168
169
170.. exception:: Incomplete
171
172   Exception raised on incomplete data. These are usually not programming errors,
173   but may be handled by reading a little more data and trying again.
174
175
176.. seealso::
177
178   Module :mod:`base64`
179      Support for RFC compliant base64-style encoding in base 16, 32, 64,
180      and 85.
181
182   Module :mod:`uu`
183      Support for UU encoding used on Unix.
184
185   Module :mod:`quopri`
186      Support for quoted-printable encoding used in MIME email messages.
187