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
– Ωmega, Commented Jul 27, 2012 at 20:31

Julian · Accepted Answer · 2012-07-27 20:48:23Z

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, 2012 at 20:48

answered Jul 27, 2012 at 20:30

Julian

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6 Comments

daydreamer Over a year ago

Is there a way to match the literal string with pattern?

Julian Over a year ago

Neither does saying "that doesn't helps out".

daydreamer Over a year ago

sorry if you feel bad, but yeah I tried the way you said and it doesn't work

Julian Over a year ago

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".

daydreamer Over a year ago

ah, sorry about that, I am continuously making updates to code above

|

Ωmega · Accepted Answer · 2012-07-27 21:00:35Z

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, 2012 at 21:00

Ωmega

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1 Comment

Ωmega Over a year ago

Check also stackoverflow.com/questions/1035340/…

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