Python: How do I make this regex work when Input is read from file

Question

>>> line = '\xc2d sdsdfdslkfsdkfjdsf'
>>> pattern_strings = ['\xc2d', '\xe9']
>>> pattern = '|'.join(pattern_strings)
>>> pattern
'\xc2d|\xe9'
>>> import re
>>> re.findall(pattern, line)
['\xc2d']

When I put line in a file and try to do the same regex, it doen't show up anything

def find_pattern(path):
    with open(path) as f:
        for line in f:
            line = line.strip()
            pattern_strings = ['\xc2d', '\xe9'] # or using ['\\xc2d', '\xe9'] doesn't help
            pattern = '|'.join(pattern_strings)
            print re.findall(pattern, line)

where path is a file looked as following
\xc2d sdsdfdslkfsdkfjdsf

I see

\xc2d
[]
d\xa0
[]
\xe7
[]
\xc3\ufffdd
[]
\xc3\ufffdd
[]
\xc2\xa0
[]
\xc3\xa7
[]
\xa0\xa0
[]
'619d813\xa03697'
[]

Add `print line` to your app to ensure you are reading file properly — Ωmega, Jul 27 '12 at 20:31

Julian · Answer 1 · 2012-07-27T20:48:23.333

2

line = "\xc2d bla" is a Python string where `"\xc2d" is a substring with 2 characters in it.

Your file sounds like it has the literal string "\xc2d" in it, which wouldn't match that pattern.

If you'd like to match the literal string, you'd need to match each of its characters (so, escape the slash).

pattern = r"\\xc2d"

edited Jul 27 '12 at 20:48

answered Jul 27 '12 at 20:30

Julian

3,375
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Is there a way to match the literal string with pattern? – daydreamer Jul 27 '12 at 20:31
Neither does saying "that doesn't helps out". – Julian Jul 27 '12 at 20:37
sorry if you feel bad, but yeah I tried the way you said and it doesn't work – daydreamer Jul 27 '12 at 20:38
1

I don't feel bad :). If you'd like help, you need to specify what you tried, and how it didn't work. Just saying "it didn't work" isn't helpful, nor is responding with "what you told me isn't helpful". – Julian Jul 27 '12 at 20:41
ah, sorry about that, I am continuously making updates to code above – daydreamer Jul 27 '12 at 20:45
Oh. Well, you're using non-raw strings, so you need to escape the pattern I gave you, or use a raw string. Edited again to show the latter. – Julian Jul 27 '12 at 20:48

score 1 · Answer 2 · answered Jul 27 '12 at 21:00

1

You would need to read file in binary mode f = open("myfile", "rb") to prevent \x conversion, as in Python \xhh represents hex escape characters.

Non-binary reading will fail - check here.

answered Jul 27 '12 at 21:00

Ωmega

42,614
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203

Check also http://stackoverflow.com/questions/1035340/reading-binary-file-in-python – Ωmega Jul 27 '12 at 21:04

Python: How do I make this regex work when Input is read from file

2 Answers2