2 :mod:`base64` --- RFC 3548: Base16, Base32, Base64 Data Encodings
3 =================================================================
6 :synopsis: RFC 3548: Base16, Base32, Base64 Data Encodings
10 pair: base64; encoding
11 single: MIME; base64 encoding
13 This module provides data encoding and decoding as specified in :rfc:`3548`.
14 This standard defines the Base16, Base32, and Base64 algorithms for encoding and
15 decoding arbitrary binary strings into text strings that can be safely sent by
16 email, used as parts of URLs, or included as part of an HTTP POST request. The
17 encoding algorithm is not the same as the :program:`uuencode` program.
19 There are two interfaces provided by this module. The modern interface supports
20 encoding and decoding string objects using all three alphabets. The legacy
21 interface provides for encoding and decoding to and from file-like objects as
22 well as strings, but only using the Base64 standard alphabet.
24 The modern interface, which was introduced in Python 2.4, provides:
27 .. function:: b64encode(s[, altchars])
29 Encode a string use Base64.
31 *s* is the string to encode. Optional *altchars* must be a string of at least
32 length 2 (additional characters are ignored) which specifies an alternative
33 alphabet for the ``+`` and ``/`` characters. This allows an application to e.g.
34 generate URL or filesystem safe Base64 strings. The default is ``None``, for
35 which the standard Base64 alphabet is used.
37 The encoded string is returned.
40 .. function:: b64decode(s[, altchars])
42 Decode a Base64 encoded string.
44 *s* is the string to decode. Optional *altchars* must be a string of at least
45 length 2 (additional characters are ignored) which specifies the alternative
46 alphabet used instead of the ``+`` and ``/`` characters.
48 The decoded string is returned. A :exc:`TypeError` is raised if *s* were
49 incorrectly padded or if there are non-alphabet characters present in the
53 .. function:: standard_b64encode(s)
55 Encode string *s* using the standard Base64 alphabet.
58 .. function:: standard_b64decode(s)
60 Decode string *s* using the standard Base64 alphabet.
63 .. function:: urlsafe_b64encode(s)
65 Encode string *s* using a URL-safe alphabet, which substitutes ``-`` instead of
66 ``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet. The result
67 can still contain ``=``.
70 .. function:: urlsafe_b64decode(s)
72 Decode string *s* using a URL-safe alphabet, which substitutes ``-`` instead of
73 ``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet.
76 .. function:: b32encode(s)
78 Encode a string using Base32. *s* is the string to encode. The encoded string
82 .. function:: b32decode(s[, casefold[, map01]])
84 Decode a Base32 encoded string.
86 *s* is the string to decode. Optional *casefold* is a flag specifying whether a
87 lowercase alphabet is acceptable as input. For security purposes, the default
90 :rfc:`3548` allows for optional mapping of the digit 0 (zero) to the letter O
91 (oh), and for optional mapping of the digit 1 (one) to either the letter I (eye)
92 or letter L (el). The optional argument *map01* when not ``None``, specifies
93 which letter the digit 1 should be mapped to (when *map01* is not ``None``, the
94 digit 0 is always mapped to the letter O). For security purposes the default is
95 ``None``, so that 0 and 1 are not allowed in the input.
97 The decoded string is returned. A :exc:`TypeError` is raised if *s* were
98 incorrectly padded or if there are non-alphabet characters present in the
102 .. function:: b16encode(s)
104 Encode a string using Base16.
106 *s* is the string to encode. The encoded string is returned.
109 .. function:: b16decode(s[, casefold])
111 Decode a Base16 encoded string.
113 *s* is the string to decode. Optional *casefold* is a flag specifying whether a
114 lowercase alphabet is acceptable as input. For security purposes, the default
117 The decoded string is returned. A :exc:`TypeError` is raised if *s* were
118 incorrectly padded or if there are non-alphabet characters present in the
121 The legacy interface:
124 .. function:: decode(input, output)
126 Decode the contents of the *input* file and write the resulting binary data to
127 the *output* file. *input* and *output* must either be file objects or objects
128 that mimic the file object interface. *input* will be read until
129 ``input.read()`` returns an empty string.
132 .. function:: decodestring(s)
134 Decode the string *s*, which must contain one or more lines of base64 encoded
135 data, and return a string containing the resulting binary data.
138 .. function:: encode(input, output)
140 Encode the contents of the *input* file and write the resulting base64 encoded
141 data to the *output* file. *input* and *output* must either be file objects or
142 objects that mimic the file object interface. *input* will be read until
143 ``input.read()`` returns an empty string. :func:`encode` returns the encoded
144 data plus a trailing newline character (``'\n'``).
147 .. function:: encodestring(s)
149 Encode the string *s*, which can contain arbitrary binary data, and return a
150 string containing one or more lines of base64-encoded data.
151 :func:`encodestring` returns a string containing one or more lines of
152 base64-encoded data always including an extra trailing newline (``'\n'``).
154 An example usage of the module:
157 >>> encoded = base64.b64encode('data to be encoded')
159 'ZGF0YSB0byBiZSBlbmNvZGVk'
160 >>> data = base64.b64decode(encoded)
167 Module :mod:`binascii`
168 Support module containing ASCII-to-binary and binary-to-ASCII conversions.
170 :rfc:`1521` - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies
171 Section 5.2, "Base64 Content-Transfer-Encoding," provides the definition of the