\section{\module{base64} ---	 RFC 3548: Base16, Base32, Base64 Data Encodings} \declaremodule{standard}{base64}\modulesynopsis{RFC 3548: Base16, Base32, Base64 Data Encodings}  \indexii{base64}{encoding}\index{MIME!base64 encoding} This module provides data encoding and decoding as specified in\rfc{3548}.  This standard defines the Base16, Base32, and Base64algorithms for encoding and decoding arbitrary binary strings intotext 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 isnot the same as the \program{uuencode} program. There are two interfaces provided by this module.  The moderninterface supports encoding and decoding string objects using allthree alphabets.  The legacy interface provides for encoding anddecoding to and from file-like objects as well as strings, but onlyusing the Base64 standard alphabet. The modern interface, which was introduced in Python 2.4, provides: \begin{funcdesc}{b64encode}{s\optional{, altchars}}Encode a string use Base64. \var{s} is the string to encode.  Optional \var{altchars} must be astring of at least length 2 (additional characters are ignored) whichspecifies an alternative alphabet for the \code{+} and \code{/}characters.  This allows an application to e.g. generate URL orfilesystem safe Base64 strings.  The default is \code{None}, for whichthe standard Base64 alphabet is used. The encoded string is returned.\end{funcdesc} \begin{funcdesc}{b64decode}{s\optional{, altchars}}Decode a Base64 encoded string. \var{s} is the string to decode.  Optional \var{altchars} must be astring of at least length 2 (additional characters are ignored) whichspecifies the alternative alphabet used instead of the \code{+} and\code{/} characters. The decoded string is returned.  A \exception{TypeError} is raised if\var{s} were incorrectly padded or if there are non-alphabetcharacters present in the string.\end{funcdesc} \begin{funcdesc}{standard_b64encode}{s}Encode string \var{s} using the standard Base64 alphabet.\end{funcdesc} \begin{funcdesc}{standard_b64decode}{s}Decode string \var{s} using the standard Base64 alphabet.\end{funcdesc} \begin{funcdesc}{urlsafe_b64encode}{s}Encode string \var{s} using a URL-safe alphabet, which substitutes\code{-} instead of \code{+} and \code{_} instead of \code{/} in thestandard Base64 alphabet.\end{funcdesc} \begin{funcdesc}{urlsafe_b64decode}{s}Decode string \var{s} using a URL-safe alphabet, which substitutes\code{-} instead of \code{+} and \code{_} instead of \code{/} in thestandard Base64 alphabet.\end{funcdesc} \begin{funcdesc}{b32encode}{s}Encode a string using Base32.  \var{s} is the string to encode.  Theencoded string is returned.\end{funcdesc} \begin{funcdesc}{b32decode}{s\optional{, casefold\optional{, map01}}}Decode a Base32 encoded string. \var{s} is the string to decode.  Optional \var{casefold} is a flagspecifying whether a lowercase alphabet is acceptable as input.  Forsecurity purposes, the default is \code{False}. \rfc{3548} allows for optional mapping of the digit 0 (zero) to theletter O (oh), and for optional mapping of the digit 1 (one) to eitherthe letter I (eye) or letter L (el).  The optional argument\var{map01} when not \code{None}, specifies which letter the digit 1 shouldbe mapped to (when map01 is not \var{None}, the digit 0 is alwaysmapped to the letter O).  For security purposes the default is\code{None}, so that 0 and 1 are not allowed in the input. The decoded string is returned.  A \exception{TypeError} is raised if\var{s} were incorrectly padded or if there are non-alphabet characterspresent in the string.\end{funcdesc} \begin{funcdesc}{b16encode}{s}Encode a string using Base16. \var{s} is the string to encode.  The encoded string is returned.\end{funcdesc} \begin{funcdesc}{b16decode}{s\optional{, casefold}}Decode a Base16 encoded string. \var{s} is the string to decode.  Optional \var{casefold} is a flagspecifying whether a lowercase alphabet is acceptable as input.  Forsecurity purposes, the default is \code{False}. The decoded string is returned.  A \exception{TypeError} is raised if\var{s} were incorrectly padded or if there are non-alphabetcharacters present in the string.\end{funcdesc} The legacy interface: \begin{funcdesc}{decode}{input, output}Decode the contents of the \var{input} file and write the resultingbinary data to the \var{output} file.\var{input} and \var{output} must either be file objects or objects thatmimic the file object interface. \var{input} will be read until\code{\var{input}.read()} returns an empty string.\end{funcdesc} \begin{funcdesc}{decodestring}{s}Decode the string \var{s}, which must contain one or more lines ofbase64 encoded data, and return a string containing the resultingbinary data.\end{funcdesc} \begin{funcdesc}{encode}{input, output}Encode the contents of the \var{input} file and write the resultingbase64 encoded data to the \var{output} file.\var{input} and \var{output} must either be file objects or objects thatmimic the file object interface. \var{input} will be read until\code{\var{input}.read()} returns an empty string.  \function{encode()}returns the encoded data plus a trailing newline character(\code{'\e n'}).\end{funcdesc} \begin{funcdesc}{encodestring}{s}Encode the string \var{s}, which can contain arbitrary binary data,and return a string containing one or more lines ofbase64-encoded data.  \function{encodestring()} returns astring containing one or more lines of base64-encoded dataalways including an extra trailing newline (\code{'\e n'}).\end{funcdesc} An example usage of the module: \begin{verbatim}>>> import base64>>> encoded = base64.b64encode('data to be encoded')>>> encoded'ZGF0YSB0byBiZSBlbmNvZGVk'>>> data = base64.b64decode(encoded)>>> data'data to be encoded'\end{verbatim} \begin{seealso}  \seemodule{binascii}{Support module containing \ASCII-to-binary                       and binary-to-\ASCII{} conversions.}  \seerfc{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.}\end{seealso}