| :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) |
| |
| 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 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:: 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. |
| |
| |
| .. 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. |
| |