Using Python regular expressions how can you get a True/False returned? All Python returns is:
<_sre.SRE_Match object at ...>
6 Answers
If you really need True or False, just use bool
>>> bool(re.search("hi", "abcdefghijkl"))
True
>>> bool(re.search("hi", "abcdefgijkl"))
False
As other answers have pointed out, if you are just using it as a condition for an if or while, you can use it directly without wrapping in bool()
6 Comments
Aizzat Suhardi
bool value is needed when the conditional statement contains boolean arithmetic operation. eg: if (re.search("a","abc") & True):
John La Rooy
@AizzatSuhardi,
& is a bitwise operaration. and would be the boolean operation.Aizzat Suhardi
thanks @JohnLaRooy. correction:
(re.search("a","abc") and True)
Guilherme Salome
Wrapping in
bool makes the intention of the programmer clear to the reader.
DannyMoshe
This is not just clearer, in some cases necessary i.e. if you are using the assertTrue function in python unit test to check a regex match (you need a boolean value, not expression). Or any function where you need a boolean input...
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Match objects are always true, and None is returned if there is no match. Just test for trueness.
if re.match(...):
answered Jul 5, 2011 at 0:01
Ignacio Vazquez-Abrams
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8 Comments
Yu Shen
re.match(...) would return true if the string's beginning part match the regular pattern. While search will confirm the pattern anywhere in the string.
NuclearPeon
It may be more desirable to use
if re.match(...) is None: instead
Charlie Parker
sorry, did you address the comments in your answer? Its unclear to me, do you mind clarifying?
ytu
May I ask why
re is designed like this? If match objects are always true, why doesn't it just return True at the first place, given that we always need to know whether the answer is true or false anyway?
Ignacio Vazquez-Abrams
@ytu: Because then you can do everything else you need to.
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Here is my method:
import re
# Compile
p = re.compile(r'hi')
# Match and print
print bool(p.match("abcdefghijkl"))
Ignacio Vazquez-Abrams is correct. But to elaborate, re.match() will return either None, which evaluates to False, or a match object, which will always be True as he said. Only if you want information about the part(s) that matched your regular expression do you need to check out the contents of the match object.
Comments
One way to do this is just to test against the return value. Because you're getting <_sre.SRE_Match object at ...> it means that this will evaluate to true. When the regular expression isn't matched you'll the return value None, which evaluates to false.
import re
if re.search("c", "abcdef"):
print "hi"
Produces hi as output.
2 Comments
Ignacio Vazquez-Abrams
You always get a return value;
None is the default if nothing is explicitly returned.
Gavin Anderegg
Thanks -- corrected that. I was just going by what I saw in the REPL.
You can use re.match() or re.search().
Python offers two different primitive operations based on regular expressions: re.match() checks for a match only at the beginning of the string, while re.search() checks for a match anywhere in the string (this is what Perl does by default). refer this
answered Oct 16, 2019 at 5:30
Sashini Hettiarachchi
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bool(re.search(pattern=META_VAR_REGEX, string=coq_str)).