What is the difference between the search()
and match()
functions in the Python re
module?
I’ve read the Python 2 documentation (Python 3 documentation), but I never seem to remember it. I keep having to look it up and re-learn it. I’m hoping that someone will answer it clearly with examples so that (perhaps) it will stick in my head. Or at least I’ll have a better place to return with my question and it will take less time to re-learn it.
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Answer
re.match
is anchored at the beginning of the string. That has nothing to do with newlines, so it is not the same as using ^
in the pattern.
As the re.match documentation says:
If zero or more characters at the beginning of string match the regular expression pattern, return a corresponding
MatchObject
instance. ReturnNone
if the string does not match the pattern; note that this is different from a zero-length match.Note: If you want to locate a match anywhere in string, use
search()
instead.
re.search
searches the entire string, as the documentation says:
Scan through string looking for a location where the regular expression pattern produces a match, and return a corresponding
MatchObject
instance. ReturnNone
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.
So if you need to match at the beginning of the string, or to match the entire string use match
. It is faster. Otherwise use search
.
The documentation has a specific section for match
vs. search
that also covers multiline strings:
Python offers two different primitive operations based on regular expressions:
match
checks for a match only at the beginning of the string, whilesearch
checks for a match anywhere in the string (this is what Perl does by default).Note that
match
may differ fromsearch
even when using a regular expression beginning with'^'
:'^'
matches only at the start of the string, or inMULTILINE
mode also immediately following a newline. The “match
” operation succeeds only if the pattern matches at the start of the string regardless of mode, or at the starting position given by the optionalpos
argument regardless of whether a newline precedes it.
Now, enough talk. Time to see some example code:
# example code: string_with_newlines = """something someotherthing""" import re print re.match('some', string_with_newlines) # matches print re.match('someother', string_with_newlines) # won't match print re.match('^someother', string_with_newlines, re.MULTILINE) # also won't match print re.search('someother', string_with_newlines) # finds something print re.search('^someother', string_with_newlines, re.MULTILINE) # also finds something m = re.compile('thing$', re.MULTILINE) print m.match(string_with_newlines) # no match print m.match(string_with_newlines, pos=4) # matches print m.search(string_with_newlines, re.MULTILINE) # also matches