Python - delete uuencoding lines

Question

I am processing many text files which (some of them) contain uuencoding which can be .jpg or .pdf or .zip of .xlsx etc. I don't care about the embedded UUencoded data, so I would just like to discard these passages and keep the rest of the text. I'm struggling with how to come up with a method to skip only just enough, but not too much.

To summarize http://en.wikipedia.org/wiki/Uuencoding each blob begins with

begin 644 filename.extension

every line after the begin 644 seems to start by the letter

M

so this might also help. Any idea how to have a function that deletes all these lines for all .txt files in a folder (directory)?

For example, the following is a .jpg uuencoding

GRAPHIC
18
g438975g32h99a01.jpg

begin 644 g438975g32h99a01.jpg
M_]C_X``02D9)1@`!`@$`8`!@``#_[0G64&AO;=&]S:&]P(#,N,``X0DE-`^T`
M`````!``8`````$``0!@`````0`!.$))300-```````$````'CA"24T$&0``
M````!````!XX0DE-`_,```````D```````````$`.$))300*```````!```X
M0DE-)Q````````H``0`````````".$))30/U``````!(`"]F9@`!`&QF9;@`&
M```````!`"]F9@`!`*&9F@`&```````!`#(````!`%H````&```````!`#4`
M```!`"T````&```````!.$))30/X``````!P``#_____________________
M________`^@`````_____________________________P/H`````/______
M______________________\#Z`````#_____________________________
M`^@``#A"24T$"```````$`````$```)````"0``````X0DE-!!X```````0`
M````.$))300:``````!M````!@``````````````)P```+`````&`&<`,P`R
M`&@`.0`Y`````0`````````````````````````!``````````````"P````
M)P`````````````````````````````````````````````X0DE-!!$`````
M``$!`#A"24T$%```````!`````(X0DE-!`P`````!SH````!````<````!D`
M``%0```@T```!QX`&``!_]C_X``02D9)1@`!`@$`2`!(``#_[@`.061O8F4`
M9(`````!_]L`A``,"`@("0@,"0D,$0L*"Q$5#PP,#Q48$Q,5$Q,8$0P,#`P,
M#!$,#`P,#`P,#`P,#`P,#`P,#`P,#`P,#`P,#`P,`0T+"PT.#1`.#A`4#@X.
M%!0.#@X.%!$,#`P,#!$1#`P,#`P,$0P,#`P,#`P,#`P,#`P,#`P,#`P,#`P,
M#`P,#`S_P``1"``9`'`#`2(``A$!`Q$!_]T`!``'_\0!/P```04!`0$!`0$`
M`````````P`!`@0%!@<("0H+`0`!!0$!`0$!`0`````````!``(#!`4&!P@)
M"@L0``$$`0,"!`(%!P8(!0,,,P$``A$#!"$2,05!46$3(G&!,@84D:&Q0B;,D
M%5+!8C,T<H+10P)E\K.$P]-U
MX_-&)Y2DA;25Q-3D]*6UQ=7E]59F=H:6IK;&UN;V-T=79W>'EZ>WQ]?G]Q$`
M`@(!`@0$`P0%!@<'!@4U`0`"$0,A,1($05%A<2(3!3*!D12AL4(CP5+1\#,D
M8N%R@I)#4Q5C<S3Q)086HK*#!R8UPM)$DU2C%V1%539T9>+RLX3#TW7C\T:4
MI(6TE<34Y/2EM<75Y?569G:&EJ;:VQM;F]B

I would like to be left with just

GRAPHIC
18
g438975g32h99a01.jpg

For background, see also my earlier question How to remove weird encoding from txt file

EDIT : Here is a try

start_marker = 'begin 644'

with open('fileWithBegin644.txt') as inf:
    ignoreLines = False
    for line in inf:
        if start_marker in line:
            print line,
            ignoreLines = True         
        if not ignoreLines:
    with open("strip_" + inf, "w") as f: 
        f.write(line.get_text().encode('utf-8'))

But I am getting the following error

  File "removeUuencodingFromAll.py", line 10
    with open("strip_" + inf, "w") as f: 
    ^
IndentationError: expected an indented block

Answer 1

I coded up what was supposed to be a rather simple generator. Because the spec is slightly tedious (why two separate end markers on different lines?) it is rather bulky, but here goes. It should work as a validator for uuencode at the same time, but I have only tested it in very limited settings.

import re

def unuuencode (iterator, collector=None, ignore_length_errors=False):
    """
    Yield lines from iterator except when they are in an uuencode blob.

    If collector is not None, append to it the uuencoded blobs as a list
    of a list of lines, one for each uuencoded blob.
    """
    state = None  # one of { None, 'in_blob', 'closing', 'closed' }
    collectitem = None
    regex = re.compile(r'^begin\s+[0-7]{3,6}\s+.*?(?:\r?\n)?$')

    for line in iterator:
        if state == None:
            if regex.match(line):
                if collector != None:
                    collectitem = [line]
                state = 'in_blob'
                continue
            else:
                yield line

        else:
            stripped = line.rstrip('\r\n')

            if state == 'in_blob' and line.startswith('`'):
                state = 'closing'

            if state == 'closing':
                if stripped != '`':
                    raise ValueError('Expected "`" but got "%s"' % line)
                state = 'closed'
            elif state == 'closed':
                if stripped != 'end':
                    raise ValueError('Expected "end" but got "%s"' % line)
                state = None
            else:
                expect = ord(line[0:1])-32
                actual = len(stripped)
                seen = (len(stripped)-1)*6/8
                if seen != expect:
                    if not ignore_length_errors:
                        raise ValueError('Wrong prefix on line: %s '
                            '(indicated %i, 6/8 %i, actual length %i)' % (
                                line, expect, seen, actual))
                if line[0:1] != 'M':
                    state = 'closing'

            if collectitem:
                collectitem.append(line)

            if state is None:
                if collectitem:
                    collector.append(collectitem)
                    collectitem = None

            continue

Use it like this:

with open(file, 'r') as f:
    lines = [x for x in unuuencode(f)]

or like this:

with open(file, 'r') as f:
    blobs = []
    lines = [x for x in unuuencode(f, collector=blobs)]

or like this:

with open(file, 'r') as f:
    lines = f.read().split('\n')
# ... or whichever way you obtained your content as an array of lines
lines = [x for x in unuuencode(lines)]

or in the case of the code you seem to be using:

for fi in sys.argv[1:]:
    with open(fi) as markup:
        soup = BeautifulSoup(''.join(unuuencode(markup, ignore_length_errors=True)))
    with open("strip_" + fi, "w") as f:
        f.write(soup.get_text().encode('utf-8'))

The sample you linked to had an invalid length indicator in the second uuencoded blob, so I added an option to ignore that.