CODEWITHSUNDEEP
pythonregex
Mike
Mike

Reputation: 1844

Python Regex Search Always False?

I'm pretty sure I'm missing something very elementary here as I'm normally ok with Python & Regex. I'm looking to see if the string supplied contains at least one number, and this is the command line I'm going through, but always getting false...

>>> import re
>>> test_string = "123567890"
>>> pat = re.compile("[0-9]")
>>> pat.search(test_string) == True
False

Before posting this I've tried a few other permutations and not getting very far, what am I doing wrong?

Upvotes: 1

Views: 860

Answers (4)

Greg E.
Greg E.

Reputation: 2742

The problem is that the re.search() method does not actually return a bool, it returns a specialized regexp. match object. bool(pat.search(test_string)) should return True, viz.:

>>> import re
>>> test_string = "123567890"
>>> pat = re.compile("[0-9]")
>>> bool(pat.search(test_string))
True

The normal way to check for a successful match is simply to use the if construct, i.e.:

>>> if pat.search(test_string): True
... 
True

You can use this abbreviated form of truth-testing for any object that implements one of either the __nonzero__ or __len__ special methods.

Upvotes: 0

Levon
Levon

Reputation: 143047

pat.search doesn't return a Boolean value but a MatchObject so your comparison will fail:

In [9]: p = pat.search(test_string)

In [10]: p
Out[10]: <_sre.SRE_Match at 0x3cfa608>

In [11]: type(p)
Out[11]: _sre.SRE_Match

See re.search docs:

re.search(pattern, string, flags=0)

Scan through string looking for a location where the regular expression pattern produces a match, and return a corresponding MatchObject instance. Return None if no position in the string matches the pattern; note that this is different from finding a zero-length match at some point in the string.

Upvotes: 4

robert
robert

Reputation: 34398

Here's how you should use match objects. I normally need more than a True/False from a match object, so I always save it away.

>>> m = pat.search(test_string)
>>> bool(m) == True
True
>>> if m:
        print "true"
true

Upvotes: 0

Sean Johnson
Sean Johnson

Reputation: 5607

re.search returns a MatchObject when it finds a match, not a boolean. It DOES return None when it doesn't match, so this would do what you're trying to do:

pat.search(test_string)!=None

Upvotes: 0

Related Questions