Split a string at uppercase letters

Unfortunately it's not possible to split on a zero-width match in Python. But you can use re.findall instead:

>>> import re
>>> re.findall('[A-Z][^A-Z]*', 'TheLongAndWindingRoad')
['The', 'Long', 'And', 'Winding', 'Road']
>>> re.findall('[A-Z][^A-Z]*', 'ABC')
['A', 'B', 'C']

Here is an alternative regex solution. The problem can be reprased as "how do I insert a space before each uppercase letter, before doing the split":

>>> s = "TheLongAndWindingRoad ABC A123B45"
>>> re.sub( r"([A-Z])", r" \1", s).split()
['The', 'Long', 'And', 'Winding', 'Road', 'A', 'B', 'C', 'A123', 'B45']

This has the advantage of preserving all non-whitespace characters, which most other solutions do not.