Python regex multiple search

Question

I need to search a string for multiple words.

import re

words = [{'word':'test1', 'case':False}, {'word':'test2', 'case':False}]

status = "test1 test2"

for w in words:
    if w['case']:
        r = re.compile("\s#?%s" % w['word'], re.IGNORECASE|re.MULTILINE)
    else:
        r = re.compile("\s#?%s" % w['word'], re.MULTILINE)
    if r.search(status):
        print "Found word %s" % w['word']

For some reason, this will only ever find "test2" and never "test1". Why is this?

I know I can use | delimitated searches but there could be hundreds of words which is why I am using a for loop.

Martijn Pieters · Accepted Answer · 2011-05-28 18:29:52Z

9

There is no space before test1 in status, while your generated regular expressions require there to be a space.

You can modify the test to match either after a space or at the beginning of a line:

for w in words:
    if w['case']:
        r = re.compile("(^|\s)#?%s" % w['word'], re.IGNORECASE|re.MULTILINE)
    else:
        r = re.compile("(^|\s)#?%s" % w['word'], re.MULTILINE)
    if r.search(status):
        print "Found word %s" % w['word']

answered May 28, 2011 at 18:29

Martijn Pieters

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3 Comments

MRAB Over a year ago

It's recommended to use raw strings when the string contains backslashes.

Hanpan Over a year ago

Thanks, not sure how I missed that.

Martijn Pieters Over a year ago

@MRAB I focused on the immediate problem; there are a number of other improvements possible (such as a flags variable to remove the redundant re.compile line.

Norbert P. · Accepted Answer · 2011-05-28 23:12:09Z

2

As Martijn pointed out, there's no space before test1. But also your code doesn't properly handle the case when a word is longer. Your code would find test2blabla as an instance of test2, and I'm not sure if that is what you want.

I suggest using word boundary regex \b:

for w in words:
    if w['case']:
        r = re.compile(r"\b%s\b" % w['word'], re.IGNORECASE|re.MULTILINE)
    else:
        r = re.compile(r"\b%s\b" % w['word'], re.MULTILINE)
    if r.search(status):
        print "Found word %s" % w['word']

EDIT:

I should've pointed out that if you really want to allow only (whitespace)word or (whitespace)#word format, you cannot use \b.

edited May 28, 2011 at 23:12

answered May 28, 2011 at 18:41

Norbert P.

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3 Comments

Martijn Pieters Over a year ago

You are missing the #? from the original test.

Norbert P. Over a year ago

Fair enough. But since that didn't make a difference for the test string, I dropped it. Of course, it interferes with the word boundary.

Martijn Pieters Over a year ago

Isn't that a rather important detail then?

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