4.14 The uu Module

The uu encoding scheme is used to convert arbitrary binary data to plain text. This format is quite popular on the Usenet, but is slowly being superseded by base64 encoding.

A uu encoder takes groups of three bytes (24 bits) and converts each group to a sequence of four printable characters (6 bits per character), using characters from chr(32) (space) to chr(95). Including the length marker and line feed characters, uu encoding typically expands data by 40 percent.

An encoded data stream starts with a begin line, which includes the file privileges (the Unix mode field as an octal number) and the filename, and ends with an end line:

begin 666 sample.jpg
M_]C_X  02D9)1@ ! 0   0 !  #_VP!#  @&!@<&!0@'!P<)'0@*#!0-# L+
...more lines like this...
end

The uu module provides two functions: encode and decode.

The encode(infile, outfile, filename) function, shown in Example 4-24, encodes data from the input file and writes it to the output file. The input and output file arguments can be either filenames or file objects. The third argument is used as filename in the begin field.

Example 4-24. Using the uu Module to Encode a Binary File

File: uu-example-1.py

import uu
import os, sys

infile = "samples/sample.jpg"

uu.encode(infile, sys.stdout, os.path.basename(infile))

begin 666 sample.jpg
M_]C_X  02D9)1@ ! 0   0 !  #_VP!#  @&!@<&!0@'!P<)"0@*#!0-# L+
M#!D2$P\4'1H?'AT:'!P@)"XG("(L(QP<*#<I+# Q-#0T'R<Y/3@R/"XS-#+_
MVP!# 0D)"0P+#!@-#1@R(1PA,C(R,C(R,C(R,C(R,C(R,C(R,C(R,C(R,C(R
M,C(R,C(R,C(R,C(R,C(R,C(R,C(R,C+_P  1" "  ( # 2(  A$! Q$!_\0 
M'P   04! 0$! 0$           $" P0%!@<("0H+_\0 M1   @$# P($ P4%

The decode(infile, outfile) function, shown in Example 4-25, decodes uu-encoded data from the input text file and writes it to the output file. Again, both arguments can be either filenames or file objects.

Example 4-25. Using the uu Module to Decode a uu-Encoded File

File: uu-example-2.py

import uu
import StringIO

infile = "samples/sample.uue"
outfile = "samples/sample.jpg"

#
# decode

fi = open(infile)
fo = StringIO.StringIO()

uu.decode(fi, fo)

#
# compare with original data file

data = open(outfile, "rb").read()

if fo.getvalue() == data:
    print len(data), "bytes ok"