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+
+: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 text 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 string objects using all three alphabets. The legacy
+interface provides for encoding and decoding to and from file-like objects as
+well as strings, but only using the Base64 standard alphabet.
+
+The modern interface, which was introduced in Python 2.4, provides:
+
+
+.. function:: b64encode(s[, altchars])
+
+ Encode a string use 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 string is returned.
+
+
+.. function:: b64decode(s[, altchars])
+
+ Decode a Base64 encoded string.
+
+ *s* is the 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:`TypeError` is raised if *s* were
+ incorrectly padded or if there are non-alphabet characters present in the
+ string.
+
+
+.. function:: standard_b64encode(s)
+
+ Encode string *s* using the standard Base64 alphabet.
+
+
+.. function:: standard_b64decode(s)
+
+ Decode string *s* using the standard Base64 alphabet.
+
+
+.. function:: urlsafe_b64encode(s)
+
+ Encode string *s* using a URL-safe alphabet, which substitutes ``-`` instead of
+ ``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet.
+
+
+.. function:: urlsafe_b64decode(s)
+
+ Decode string *s* using a URL-safe alphabet, which substitutes ``-`` instead of
+ ``+`` and ``_`` instead of ``/`` in the standard Base64 alphabet.
+
+
+.. function:: b32encode(s)
+
+ Encode a string using Base32. *s* is the string to encode. The encoded string
+ is returned.
+
+
+.. function:: b32decode(s[, casefold[, map01]])
+
+ Decode a Base32 encoded 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``.
+
+ :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 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 string using Base16.
+
+ *s* is the string to encode. The encoded string is returned.
+
+
+.. function:: b16decode(s[, casefold])
+
+ Decode a Base16 encoded 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 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 *input* file and write the resulting binary data to
+ the *output* file. *input* and *output* must either be file objects or objects
+ that mimic the file object interface. *input* will be read until
+ ``input.read()`` returns an empty string.
+
+
+.. function:: decodestring(s)
+
+ Decode the string *s*, which must contain one or more lines of base64 encoded
+ data, and return a string containing the resulting binary data.
+
+
+.. function:: encode(input, output)
+
+ Encode the contents of the *input* file and write the resulting base64 encoded
+ data to the *output* file. *input* and *output* must either be file objects or
+ objects that mimic the file object interface. *input* will be read until
+ ``input.read()`` returns an empty string. :func:`encode` returns the encoded
+ data plus a trailing newline character (``'\n'``).
+
+
+.. function:: encodestring(s)
+
+ Encode the string *s*, which can contain arbitrary binary data, and return a
+ string containing one or more lines of base64-encoded data.
+ :func:`encodestring` returns a string containing one or more lines of
+ base64-encoded data always including an extra trailing newline (``'\n'``).
+
+An example usage of the module:
+
+ >>> import base64
+ >>> encoded = base64.b64encode('data to be encoded')
+ >>> encoded
+ 'ZGF0YSB0byBiZSBlbmNvZGVk'
+ >>> data = base64.b64decode(encoded)
+ >>> data
+ '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.
+