185 lines
6.4 KiB
ReStructuredText
185 lines
6.4 KiB
ReStructuredText
:mod:`base64` --- RFC 3548: Base16, Base32, Base64 Data Encodings
|
|
=================================================================
|
|
|
|
.. module:: base64
|
|
:synopsis: RFC 3548: Base16, Base32, Base64 Data Encodings
|
|
|
|
|
|
.. index::
|
|
pair: base64; encoding
|
|
single: MIME; base64 encoding
|
|
|
|
This module provides data encoding and decoding as specified in :rfc:`3548`.
|
|
This standard defines the Base16, Base32, and Base64 algorithms for encoding
|
|
and decoding arbitrary binary strings into ASCII-only byte strings that can be
|
|
safely sent by email, used as parts of URLs, or included as part of an HTTP
|
|
POST request. The encoding algorithm is not the same as the
|
|
:program:`uuencode` program.
|
|
|
|
There are two interfaces provided by this module. The modern interface
|
|
supports encoding and decoding ASCII byte string objects using all three
|
|
alphabets. The legacy interface provides for encoding and decoding to and from
|
|
file-like objects as well as byte strings, but only using the Base64 standard
|
|
alphabet.
|
|
|
|
The modern interface provides:
|
|
|
|
.. function:: b64encode(s, altchars=None)
|
|
|
|
Encode a byte string using Base64.
|
|
|
|
*s* is the string to encode. Optional *altchars* must be a string of at least
|
|
length 2 (additional characters are ignored) which specifies an alternative
|
|
alphabet for the ``+`` and ``/`` characters. This allows an application to e.g.
|
|
generate URL or filesystem safe Base64 strings. The default is ``None``, for
|
|
which the standard Base64 alphabet is used.
|
|
|
|
The encoded byte string is returned.
|
|
|
|
|
|
.. function:: b64decode(s, altchars=None, validate=False)
|
|
|
|
Decode a Base64 encoded byte string.
|
|
|
|
*s* is the byte string to decode. Optional *altchars* must be a string of
|
|
at least length 2 (additional characters are ignored) which specifies the
|
|
alternative alphabet used instead of the ``+`` and ``/`` characters.
|
|
|
|
The decoded string is returned. A :exc:`binascii.Error` exception is raised
|
|
if *s* is incorrectly padded.
|
|
|
|
If *validate* is ``False`` (the default), non-base64-alphabet characters are
|
|
discarded prior to the padding check. If *validate* is ``True``,
|
|
non-base64-alphabet characters in the input result in a
|
|
:exc:`binascii.Error`.
|
|
|
|
|
|
.. function:: standard_b64encode(s)
|
|
|
|
Encode byte string *s* using the standard Base64 alphabet.
|
|
|
|
|
|
.. function:: standard_b64decode(s)
|
|
|
|
Decode byte string *s* using the standard Base64 alphabet.
|
|
|
|
|
|
.. function:: urlsafe_b64encode(s)
|
|
|
|
Encode byte string *s* using a URL-safe alphabet, which substitutes ``-`` instead of
|
|
``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet. The result
|
|
can still contain ``=``.
|
|
|
|
|
|
.. function:: urlsafe_b64decode(s)
|
|
|
|
Decode byte string *s* using a URL-safe alphabet, which substitutes ``-`` instead of
|
|
``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet.
|
|
|
|
|
|
.. function:: b32encode(s)
|
|
|
|
Encode a byte string using Base32. *s* is the string to encode. The encoded string
|
|
is returned.
|
|
|
|
|
|
.. function:: b32decode(s, casefold=False, map01=None)
|
|
|
|
Decode a Base32 encoded byte string.
|
|
|
|
*s* is the byte string to decode. Optional *casefold* is a flag specifying
|
|
whether a lowercase alphabet is acceptable as input. For security purposes,
|
|
the default is ``False``.
|
|
|
|
:rfc:`3548` allows for optional mapping of the digit 0 (zero) to the letter O
|
|
(oh), and for optional mapping of the digit 1 (one) to either the letter I (eye)
|
|
or letter L (el). The optional argument *map01* when not ``None``, specifies
|
|
which letter the digit 1 should be mapped to (when *map01* is not ``None``, the
|
|
digit 0 is always mapped to the letter O). For security purposes the default is
|
|
``None``, so that 0 and 1 are not allowed in the input.
|
|
|
|
The decoded byte string is returned. A :exc:`TypeError` is raised if *s* were
|
|
incorrectly padded or if there are non-alphabet characters present in the
|
|
string.
|
|
|
|
|
|
.. function:: b16encode(s)
|
|
|
|
Encode a byte string using Base16.
|
|
|
|
*s* is the string to encode. The encoded byte string is returned.
|
|
|
|
|
|
.. function:: b16decode(s, casefold=False)
|
|
|
|
Decode a Base16 encoded byte string.
|
|
|
|
*s* is the string to decode. Optional *casefold* is a flag specifying whether a
|
|
lowercase alphabet is acceptable as input. For security purposes, the default
|
|
is ``False``.
|
|
|
|
The decoded byte string is returned. A :exc:`TypeError` is raised if *s* were
|
|
incorrectly padded or if there are non-alphabet characters present in the
|
|
string.
|
|
|
|
|
|
The legacy interface:
|
|
|
|
.. function:: decode(input, output)
|
|
|
|
Decode the contents of the binary *input* file and write the resulting binary
|
|
data to the *output* file. *input* and *output* must be :term:`file objects
|
|
<file object>`. *input* will be read until ``input.read()`` returns an empty
|
|
bytes object.
|
|
|
|
|
|
.. function:: decodebytes(s)
|
|
decodestring(s)
|
|
|
|
Decode the byte string *s*, which must contain one or more lines of base64
|
|
encoded data, and return a byte string containing the resulting binary data.
|
|
``decodestring`` is a deprecated alias.
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
.. function:: encode(input, output)
|
|
|
|
Encode the contents of the binary *input* file and write the resulting base64
|
|
encoded data to the *output* file. *input* and *output* must be :term:`file
|
|
objects <file object>`. *input* will be read until ``input.read()`` returns
|
|
an empty bytes object. :func:`encode` returns the encoded data plus a trailing
|
|
newline character (``b'\n'``).
|
|
|
|
|
|
.. function:: encodebytes(s)
|
|
encodestring(s)
|
|
|
|
Encode the byte string *s*, which can contain arbitrary binary data, and
|
|
return a byte string containing one or more lines of base64-encoded data.
|
|
:func:`encodebytes` returns a string containing one or more lines of
|
|
base64-encoded data always including an extra trailing newline (``b'\n'``).
|
|
``encodestring`` is a deprecated alias.
|
|
|
|
|
|
An example usage of the module:
|
|
|
|
>>> import base64
|
|
>>> encoded = base64.b64encode(b'data to be encoded')
|
|
>>> encoded
|
|
b'ZGF0YSB0byBiZSBlbmNvZGVk'
|
|
>>> data = base64.b64decode(encoded)
|
|
>>> data
|
|
b'data to be encoded'
|
|
|
|
|
|
.. seealso::
|
|
|
|
Module :mod:`binascii`
|
|
Support module containing ASCII-to-binary and binary-to-ASCII conversions.
|
|
|
|
:rfc:`1521` - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies
|
|
Section 5.2, "Base64 Content-Transfer-Encoding," provides the definition of the
|
|
base64 encoding.
|
|
|