Determine prefix from a set of (similar) strings

Question

I have a set of strings, e.g.

my_prefix_what_ever my_prefix_what_so_ever my_prefix_doesnt_matter 

I simply want to find the longest common portion of these strings, here the prefix. In the above the result should be

my_prefix_ 

The strings

my_prefix_what_ever my_prefix_what_so_ever my_doesnt_matter 

should result in the prefix

my_ 

Is there a relatively painless way in Python to determine the prefix (without having to iterate over each character manually)?

PS: I'm using Python 2.6.3.

Answer 1

Never rewrite what is provided to you: os.path.commonprefix does exactly this:

Return the longest path prefix (taken character-by-character) that is a prefix of all paths in list. If list is empty, return the empty string (''). Note that this may return invalid paths because it works a character at a time.

For comparison to the other answers, here's the code:

# Return the longest prefix of all list elements. def commonprefix(m):     "Given a list of pathnames, returns the longest common leading component"     if not m: return ''     s1 = min(m)     s2 = max(m)     for i, c in enumerate(s1):         if c != s2[i]:             return s1[:i]     return s1