How to replace uppercase with underscore?

Question

I'm new to Python and I am trying to replace all uppercase-letters within a word to underscores, for example:

ThisIsAGoodExample

should become

this_is_a_good_example

Any ideas/tips/links/tutorials on how to achieve this?

Answer 1

Here's a regex way:

import re
example = "ThisIsAGoodExample"
print re.sub( '(?<!^)(?=[A-Z])', '_', example ).lower()

This is saying, "Find points in the string that aren't preceeded by a start of line, and are followed by an uppercase character, and substitute an underscore. Then we lower()case the whole thing.

Answer 2

import re
"_".join(l.lower() for l in re.findall('[A-Z][^A-Z]*', 'ThisIsAGoodExample'))

EDIT: Actually, this only works, if the first letter is uppercase. Otherwise this (taken from here) does the right thing:

def convert(name):
    s1 = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', s1).lower()