regexp question

[python_charmer2000]

I want to match several regexps against a large body of text. What I
have so far is similar to this:

re1 = <some regexp>
re2 = <some regexp>
re3 = <some regexp>

big_re = re.compile(re1 + '|' + re2 + '|' + re3)

matches = big_re.finditer(file_list)
for match in matches:
span = match.span()
print "matched text =", file_list[span[0]:span[1]]
print "matched re =", match.re.pattern

Now the "match.re.pattern" is the entire regexp, big_re. But I want
to print out the portion of the big re that was matched -- was it re1?
re2? or re3? Is it possible to determine this, or do I have to make
a second pass through the collection of re's and compare them against
the "matched text" in order to determine which part of the big_re was
matched?

thanks!!

 

[Ben Finney]

re1 = <some regexp>
re2 = <some regexp>
re3 = <some regexp>

big_re = re.compile(re1 + '|' + re2 + '|' + re3)

Now the "match.re.pattern" is the entire regexp, big_re. But I want
to print out the portion of the big re that was matched -- was it re1?
re2? or re3? Is it possible to determine this, or do I have to make
a second pass through the collection of re's and compare them against
the "matched text" in order to determine which part of the big_re was
matched?

That will work no matter what your regexes hapen to be, and is easily
understood. Implement that, and see if it's fast enough. (Doing
otherwise is known as "premature optimisation" and is a bad practice.)
In fact, it may be better (from a readability standpoint) to simply
compile each of the regexes and match them all each time.

An alternative, if it's not fast enough: Group the regexes and inspect
them with the re.MatchObject.group() method.
... '(' + regex1 + ')'
... + '|(' + regex2 + ')'
... + '|(' + regex3 + ')'
... )