Determining the unmatched portion of a string using a regex in Python

Question

Suppose I have a string \"a foobar\" and I use \"^a\\s*\" to match \"a \".

Is there a way to easily get \"foobar\" returned? (What was NOT matched)

I want to

Answer 1

from http://docs.python.org/library/re.html#re.split

>>> re.split('(\W+)', 'Words, words, words.')
['Words', ', ', 'words', ', ', 'words', '.', '']

so your example would be

>>> re.split(r'(^a\s*)', "a foobar")
['', 'a ', 'foobar']

at which point you can separate the odd items (your match) from the even items (the rest).

>>> l = re.split(r'(^a\s*)', "a foobar")
>>> l[1::2] # matching strings
['a ']
>>> l[::2] # non-matching strings
['', 'foobar']

This has the advantage over re.sub in that you can tell, when, where, and how many matches were found.