Question

I use Python’s re module to replace a substring, such as:

>>> import re
>>> re.sub(r"a.*b","ab","acbacbacb")
'ab'

This matches .* with cbacbac, but I want it to match c three times, so that the output is ababab.

Could anybody tell me how to do it?

Answer 1

Regex by default is greedy. Use .*?

>>> import re
>>> re.sub(r"a.*?b","ab","acbacbacb")
'ababab'
>>> 

http://docs.python.org/library/re.html

The *, +, and ? qualifiers are all greedy; they match as much
text as possible. Sometimes this behaviour isn’t desired; if the RE
<.*> is matched against '<H1>title</H1>', it will match the entire
string, and not just '<H1>'. Adding ? after the qualifier makes it
perform the match in non-greedy or minimal fashion; as few characters
as possible will be matched. Using .*? in the previous expression will
match only '<H1>'.