mirror of
https://github.com/python/cpython.git
synced 2024-12-16 21:34:44 +08:00
300 lines
10 KiB
ReStructuredText
300 lines
10 KiB
ReStructuredText
:mod:`base64` --- Base16, Base32, Base64, Base85 Data Encodings
|
|
===============================================================
|
|
|
|
.. module:: base64
|
|
:synopsis: RFC 3548: Base16, Base32, Base64 Data Encodings;
|
|
Base85 and Ascii85
|
|
|
|
**Source code:** :source:`Lib/base64.py`
|
|
|
|
.. index::
|
|
pair: base64; encoding
|
|
single: MIME; base64 encoding
|
|
|
|
--------------
|
|
|
|
This module provides functions for encoding binary data to printable
|
|
ASCII characters and decoding such encodings back to binary data.
|
|
It provides encoding and decoding functions for the encodings specified in
|
|
:rfc:`3548`, which defines the Base16, Base32, and Base64 algorithms,
|
|
and for the de-facto standard Ascii85 and Base85 encodings.
|
|
|
|
The :rfc:`3548` encodings are suitable for encoding binary data so that it can
|
|
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 :term:`bytes-like objects <bytes-like object>` to ASCII
|
|
:class:`bytes`, and decoding :term:`bytes-like objects <bytes-like object>` or
|
|
strings containing ASCII to :class:`bytes`. Both base-64 alphabets
|
|
defined in :rfc:`3548` (normal, and URL- and filesystem-safe) are supported.
|
|
|
|
The legacy interface does not support decoding from strings, but it does
|
|
provide functions for encoding and decoding to and from :term:`file objects
|
|
<file object>`. It only supports the Base64 standard alphabet, and it adds
|
|
newlines every 76 characters as per :rfc:`2045`. Note that if you are looking
|
|
for :rfc:`2045` support you probably want to be looking at the :mod:`email`
|
|
package instead.
|
|
|
|
|
|
.. versionchanged:: 3.3
|
|
ASCII-only Unicode strings are now accepted by the decoding functions of
|
|
the modern interface.
|
|
|
|
.. versionchanged:: 3.4
|
|
Any :term:`bytes-like objects <bytes-like object>` are now accepted by all
|
|
encoding and decoding functions in this module. Ascii85/Base85 support added.
|
|
|
|
The modern interface provides:
|
|
|
|
.. function:: b64encode(s, altchars=None)
|
|
|
|
Encode the :term:`bytes-like object` *s* using Base64 and return the encoded
|
|
:class:`bytes`.
|
|
|
|
Optional *altchars* must be a :term:`bytes-like object` 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.
|
|
|
|
|
|
.. function:: b64decode(s, altchars=None, validate=False)
|
|
|
|
Decode the Base64 encoded :term:`bytes-like object` or ASCII string
|
|
*s* and return the decoded :class:`bytes`.
|
|
|
|
Optional *altchars* must be a :term:`bytes-like object` or ASCII string of
|
|
at least length 2 (additional characters are ignored) which specifies the
|
|
alternative alphabet used instead of the ``+`` and ``/`` characters.
|
|
|
|
A :exc:`binascii.Error` exception is raised
|
|
if *s* is incorrectly padded.
|
|
|
|
If *validate* is ``False`` (the default), characters that are neither
|
|
in the normal base-64 alphabet nor the alternative alphabet are
|
|
discarded prior to the padding check. If *validate* is ``True``,
|
|
these non-alphabet characters in the input result in a
|
|
:exc:`binascii.Error`.
|
|
|
|
|
|
.. function:: standard_b64encode(s)
|
|
|
|
Encode :term:`bytes-like object` *s* using the standard Base64 alphabet
|
|
and return the encoded :class:`bytes`.
|
|
|
|
|
|
.. function:: standard_b64decode(s)
|
|
|
|
Decode :term:`bytes-like object` or ASCII string *s* using the standard
|
|
Base64 alphabet and return the decoded :class:`bytes`.
|
|
|
|
|
|
.. function:: urlsafe_b64encode(s)
|
|
|
|
Encode :term:`bytes-like object` *s* using the
|
|
URL- and filesystem-safe alphabet, which
|
|
substitutes ``-`` instead of ``+`` and ``_`` instead of ``/`` in the
|
|
standard Base64 alphabet, and return the encoded :class:`bytes`. The result
|
|
can still contain ``=``.
|
|
|
|
|
|
.. function:: urlsafe_b64decode(s)
|
|
|
|
Decode :term:`bytes-like object` or ASCII string *s*
|
|
using the URL- and filesystem-safe
|
|
alphabet, which substitutes ``-`` instead of ``+`` and ``_`` instead of
|
|
``/`` in the standard Base64 alphabet, and return the decoded
|
|
:class:`bytes`.
|
|
|
|
|
|
.. function:: b32encode(s)
|
|
|
|
Encode the :term:`bytes-like object` *s* using Base32 and return the
|
|
encoded :class:`bytes`.
|
|
|
|
|
|
.. function:: b32decode(s, casefold=False, map01=None)
|
|
|
|
Decode the Base32 encoded :term:`bytes-like object` or ASCII string *s* and
|
|
return the decoded :class:`bytes`.
|
|
|
|
Optional *casefold* is a flag specifying
|
|
whether a lowercase alphabet is acceptable as input. For security purposes,
|
|
the default is ``False``.
|
|
|
|
:rfc:`4648` 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.
|
|
|
|
A :exc:`binascii.Error` is raised if *s* is
|
|
incorrectly padded or if there are non-alphabet characters present in the
|
|
input.
|
|
|
|
|
|
.. function:: b32hexencode(s)
|
|
|
|
Similar to :func:`b32encode` but uses the Extended Hex Alphabet, as defined in
|
|
:rfc:`4648`.
|
|
|
|
.. versionadded:: 3.10
|
|
|
|
|
|
.. function:: b32hexdecode(s, casefold=False)
|
|
|
|
Similar to :func:`b32decode` but uses the Extended Hex Alphabet, as defined in
|
|
:rfc:`4648`.
|
|
|
|
This version does not allow the digit 0 (zero) to the letter O (oh) and digit
|
|
1 (one) to either the letter I (eye) or letter L (el) mappings, all these
|
|
characters are included in the Extended Hex Alphabet and are not
|
|
interchangable.
|
|
|
|
.. versionadded:: 3.10
|
|
|
|
|
|
.. function:: b16encode(s)
|
|
|
|
Encode the :term:`bytes-like object` *s* using Base16 and return the
|
|
encoded :class:`bytes`.
|
|
|
|
|
|
.. function:: b16decode(s, casefold=False)
|
|
|
|
Decode the Base16 encoded :term:`bytes-like object` or ASCII string *s* and
|
|
return the decoded :class:`bytes`.
|
|
|
|
Optional *casefold* is a flag specifying whether a
|
|
lowercase alphabet is acceptable as input. For security purposes, the default
|
|
is ``False``.
|
|
|
|
A :exc:`binascii.Error` is raised if *s* is
|
|
incorrectly padded or if there are non-alphabet characters present in the
|
|
input.
|
|
|
|
|
|
.. function:: a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False)
|
|
|
|
Encode the :term:`bytes-like object` *b* using Ascii85 and return the
|
|
encoded :class:`bytes`.
|
|
|
|
*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.
|
|
|
|
*wrapcol* controls whether the output should have newline (``b'\n'``)
|
|
characters added to it. If this is non-zero, each output line will be
|
|
at most this many characters long.
|
|
|
|
*pad* controls whether the input is padded to a multiple of 4
|
|
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:: 3.4
|
|
|
|
|
|
.. function:: a85decode(b, *, foldspaces=False, adobe=False, ignorechars=b' \\t\\n\\r\\v')
|
|
|
|
Decode the Ascii85 encoded :term:`bytes-like object` or ASCII string *b* and
|
|
return the decoded :class:`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 :term:`bytes-like object` or ASCII string
|
|
containing characters to ignore
|
|
from the input. This should only contain whitespace characters, and by
|
|
default contains all whitespace characters in ASCII.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
.. function:: b85encode(b, pad=False)
|
|
|
|
Encode the :term:`bytes-like object` *b* using base85 (as used in e.g.
|
|
git-style binary diffs) and return the encoded :class:`bytes`.
|
|
|
|
If *pad* is true, the input is padded with ``b'\0'`` so its length is a
|
|
multiple of 4 bytes before encoding.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
.. function:: b85decode(b)
|
|
|
|
Decode the base85-encoded :term:`bytes-like object` or ASCII string *b* and
|
|
return the decoded :class:`bytes`. Padding is implicitly removed, if
|
|
necessary.
|
|
|
|
.. versionadded:: 3.4
|
|
|
|
|
|
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.readline()`` returns an
|
|
empty bytes object.
|
|
|
|
|
|
.. function:: decodebytes(s)
|
|
|
|
Decode the :term:`bytes-like object` *s*, which must contain one or more
|
|
lines of base64 encoded data, and return the decoded :class:`bytes`.
|
|
|
|
.. 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` inserts a newline character (``b'\n'``)
|
|
after every 76 bytes of the output, as well as ensuring that the output
|
|
always ends with a newline, as per :rfc:`2045` (MIME).
|
|
|
|
|
|
.. function:: encodebytes(s)
|
|
|
|
Encode the :term:`bytes-like object` *s*, which can contain arbitrary binary
|
|
data, and return :class:`bytes` containing the base64-encoded data, with newlines
|
|
(``b'\n'``) inserted after every 76 bytes of output, and ensuring that
|
|
there is a trailing newline, as per :rfc:`2045` (MIME).
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
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.
|
|
|