Is it worth using Python's re.compile?

Question

Is there any benefit in using compile for regular expressions in Python?

h = re.compile(\'hello\')
h.match(\'hello world\')

vs

Answer 1

Performance difference aside, using re.compile and using the compiled regular expression object to do match (whatever regular expression related operations) makes the semantics clearer to Python run-time.

I had some painful experience of debugging some simple code:

compare = lambda s, p: re.match(p, s)

and later I'd use compare in

[x for x in data if compare(patternPhrases, x[columnIndex])]

where patternPhrases is supposed to be a variable containing regular expression string, x[columnIndex] is a variable containing string.

I had trouble that patternPhrases did not match some expected string!

But if I used the re.compile form:

compare = lambda s, p: p.match(s)

then in

[x for x in data if compare(patternPhrases, x[columnIndex])]

Python would have complained that "string does not have attribute of match", as by positional argument mapping in compare, x[columnIndex] is used as regular expression!, when I actually meant

compare = lambda p, s: p.match(s)

In my case, using re.compile is more explicit of the purpose of regular expression, when it's value is hidden to naked eyes, thus I could get more help from Python run-time checking.

So the moral of my lesson is that when the regular expression is not just literal string, then I should use re.compile to let Python to help me to assert my assumption.