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177 lines
6.1 KiB
177 lines
6.1 KiB
:mod:`base64` --- RFC 3548: Base16, Base32, Base64 Data Encodings
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=================================================================
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.. module:: base64
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:synopsis: RFC 3548: Base16, Base32, Base64 Data Encodings
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.. index::
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pair: base64; encoding
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single: MIME; base64 encoding
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This module provides data encoding and decoding as specified in :rfc:`3548`.
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This standard defines the Base16, Base32, and Base64 algorithms for encoding and
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decoding arbitrary binary strings into text strings that can be safely sent by
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email, used as parts of URLs, or included as part of an HTTP POST request. The
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encoding algorithm is not the same as the :program:`uuencode` program.
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There are two interfaces provided by this module. The modern interface supports
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encoding and decoding string objects using both base-64 alphabets defined
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in :rfc:`3548` (normal, and URL- and filesystem-safe). The legacy
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interface provides for encoding and decoding to and from file-like objects as
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well as strings, but only using the Base64 standard alphabet.
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The modern interface, which was introduced in Python 2.4, provides:
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.. function:: b64encode(s[, altchars])
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Encode a string using Base64.
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*s* is the string to encode. Optional *altchars* must be a string of at least
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length 2 (additional characters are ignored) which specifies an alternative
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alphabet for the ``+`` and ``/`` characters. This allows an application to e.g.
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generate URL or filesystem safe Base64 strings. The default is ``None``, for
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which the standard Base64 alphabet is used.
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The encoded string is returned.
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.. function:: b64decode(s[, altchars])
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Decode a Base64 encoded string.
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*s* is the string to decode. Optional *altchars* must be a string of at least
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length 2 (additional characters are ignored) which specifies the alternative
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alphabet used instead of the ``+`` and ``/`` characters.
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The decoded string is returned. A :exc:`TypeError` is raised if *s* is
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incorrectly padded. Characters that are neither
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in the normal base-64 alphabet nor the alternative alphabet are
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discarded prior to the padding check.
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.. function:: standard_b64encode(s)
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Encode string *s* using the standard Base64 alphabet.
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.. function:: standard_b64decode(s)
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Decode string *s* using the standard Base64 alphabet.
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.. function:: urlsafe_b64encode(s)
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Encode string *s* using the URL- and filesystem-safe
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alphabet, which substitutes ``-`` instead of
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``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet. The result
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can still contain ``=``.
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.. function:: urlsafe_b64decode(s)
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Decode string *s* using the URL- and filesystem-safe
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alphabet, which substitutes ``-`` instead of
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``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet.
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.. function:: b32encode(s)
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Encode a string using Base32. *s* is the string to encode. The encoded string
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is returned.
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.. function:: b32decode(s[, casefold[, map01]])
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Decode a Base32 encoded string.
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*s* is the string to decode. Optional *casefold* is a flag specifying whether a
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lowercase alphabet is acceptable as input. For security purposes, the default
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is ``False``.
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:rfc:`3548` allows for optional mapping of the digit 0 (zero) to the letter O
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(oh), and for optional mapping of the digit 1 (one) to either the letter I (eye)
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or letter L (el). The optional argument *map01* when not ``None``, specifies
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which letter the digit 1 should be mapped to (when *map01* is not ``None``, the
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digit 0 is always mapped to the letter O). For security purposes the default is
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``None``, so that 0 and 1 are not allowed in the input.
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The decoded string is returned. A :exc:`TypeError` is raised if *s* is
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incorrectly padded or if there are non-alphabet characters present in the
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string.
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.. function:: b16encode(s)
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Encode a string using Base16.
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*s* is the string to encode. The encoded string is returned.
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.. function:: b16decode(s[, casefold])
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Decode a Base16 encoded string.
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*s* is the string to decode. Optional *casefold* is a flag specifying whether a
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lowercase alphabet is acceptable as input. For security purposes, the default
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is ``False``.
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The decoded string is returned. A :exc:`TypeError` is raised if *s* were
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incorrectly padded or if there are non-alphabet characters present in the
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string.
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The legacy interface:
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.. function:: decode(input, output)
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Decode the contents of the *input* file and write the resulting binary data to
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the *output* file. *input* and *output* must either be file objects or objects
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that mimic the file object interface. *input* will be read until
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``input.read()`` returns an empty string.
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.. function:: decodestring(s)
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Decode the string *s*, which must contain one or more lines of base64 encoded
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data, and return a string containing the resulting binary data.
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.. function:: encode(input, output)
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Encode the contents of the *input* file and write the resulting base64 encoded
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data to the *output* file. *input* and *output* must either be file objects or
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objects that mimic the file object interface. *input* will be read until
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``input.read()`` returns an empty string. :func:`encode` returns the encoded
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data plus a trailing newline character (``'\n'``).
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.. function:: encodestring(s)
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Encode the string *s*, which can contain arbitrary binary data, and return a
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string containing one or more lines of base64-encoded data.
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:func:`encodestring` returns a string containing one or more lines of
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base64-encoded data always including an extra trailing newline (``'\n'``).
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An example usage of the module:
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>>> import base64
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>>> encoded = base64.b64encode('data to be encoded')
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>>> encoded
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'ZGF0YSB0byBiZSBlbmNvZGVk'
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>>> data = base64.b64decode(encoded)
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>>> data
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'data to be encoded'
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.. seealso::
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Module :mod:`binascii`
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Support module containing ASCII-to-binary and binary-to-ASCII conversions.
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:rfc:`1521` - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies
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Section 5.2, "Base64 Content-Transfer-Encoding," provides the definition of the
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base64 encoding.
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