Several kinds of media (e.g., email
messages) contain only text. When you want to transmit binary data
via such media, you need to encode the data as text strings. The
Python standard library supplies modules that support the standard
encodings known as Base 64, Quoted Printable, and
UU.
21.1.1 The base64 Module
The
base64 module supports the encoding specified in
RFC 1521 as Base 64. The Base 64 encoding is a compact way to
represent arbitrary binary data as text, without any attempt to
produce human-readable results. Module base64
supplies four functions.
Reads text-file-like object
infile, by calling
infile.readline until
end of file (i.e, until a call to
infile.readline returns
an empty string), decodes the Base 64-encoded text thus read, and
writes the decoded data to binary-file-like object
outfile.
Decodes text string s, which contains one
or more complete lines of Base 64-encoded text, and returns the byte
string with the corresponding decoded data.
Reads binary-file-like object infile, by
calling infile.read
(for a few bytes at a timethe amount of data that Base 64
encodes into a single output line) until end of file (i.e, until a
call to infile.read
returns an empty string). Then it encodes the data thus read in Base
64, and writes the encoded text as lines to text-file-like object
outfile. encode appends
\n to each line of text it emits, including the
last one.
Encodes binary string s, which contains
arbitrary bytes, and returns a text string with one or more complete
lines of Base 64-encoded data. encodestring always
returns a text string ending with \n.
21.1.2 The quopri Module
The
quopri module supports the encoding specified in
RFC 1521 as Quoted Printable (QP). QP can represent any binary data
as text, but it's mainly intended for data that is
textual, with a relatively modest amount of characters with the high
bit set (i.e., characters outside of the ASCII range). For such data,
QP produces results that are both compact and rather human-readable.
Module quopri supplies four functions.
decode(infile,outfile,header=False)
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Reads file-like object infile, by calling
infile.readline until
end of file (i.e, until a call to
infile.readline returns
an empty string), decodes the QP-encoded ASCII text thus read, and
writes the decoded data to file-like object
outfile. When
header is true, decode
also decodes _ (underscores) into spaces.
decodestring(s,header=False)
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Decodes string s, which contains
QP-encoded ASCII text, and returns the byte string with the decoded
data. When header is true,
decodestring also decodes _
(underscores) into spaces.
encode(infile,outfile,spaces,header=False)
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Reads file-like object infile, by calling
infile.readline until
end of file (i.e, until a call to
infile.readline returns
an empty string), encodes the data thus read in QP, and writes the
encoded ASCII text to file-like object
outfile. When
spaces is true, encode
also encodes spaces and tabs. When header
is true, encode encodes spaces as
_ (underscores).
encodestring(s,spaces=False,header=False)
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Encodes string s, which contains arbitrary
bytes, and returns a string with QP-encoded ASCII text. When
spaces is true,
encodestring also encodes spaces and tabs. When
header is true,
encodestring encodes spaces as
_ (underscores).
21.1.3 The uu Module
The uu module
supports the traditional Unix-to-Unix (UU) encoding, as implemented
by Unix programs uuencode and
uudecode. UU begins encoded data with a
begin line, which also gives the filename and
permissions of the file being encoded, and ends it with an
end line. Therefore, UU encoding lets you embed
encoded data in otherwise unstructured text, while Base 64 encoding
relies on the existence of other indications of where the encoded
data starts and finishes. Module uu supplies two
functions.
decode(infile,outfile=None,mode=None)
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Reads file-like object infile, by calling
infile.readline until
end of file (i.e, until a call to
infile.readline returns
an empty string) or until a terminator line (the string
'end' surrounded by any amount of whitespace).
decode decodes the UU-encoded text thus read, and
writes the decoded data to file-like object
outfile. When
outfile is None,
decode creates the file specified in the UU-format
begin line, with the permission bits given by
mode (the permission bits specified in the
begin line, when mode
is None). In this case, decode
raises an exception if the file already exists.
encode(infile,outfile,name='-',mode=0666)
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Reads file-like object infile, by calling
infile.read (for a few
bytes at a timethe amount of data that UU encodes into a
single output line) until end of file (i.e, until a call to
infile.read returns an
empty string). Then it encodes the data thus read in UU, and writes
the encoded text to file-like object
outfile. encode also
writes a UU begin line before the encoded text,
and a UU end line after the encoded text. In the
begin line, encode specifies
the filename as name and the mode as
mode.