Why doesn't Python's `re.split()` split on zero-length matches?
python, regex
Solution
It's a design decision that was made, and could have gone either way. Tim Peters made this post to explain:
For example, if you split "abc" by the pattern x*, what do you expect? The pattern matches (with length 0) at 4 places, but I bet most people would be surprised to get
['', 'a', 'b', 'c', '']
back instead of (as they do get)
['abc']
Some others disagree with him though. Guido van Rossum doesn't want it changed due to backwards compatibility issues. He did say:
I'm okay with adding a flag to enable this behavior though.
Edit:
There is a workaround posted by Jan Burgy:
>>> s = "Split along words, preserve punctuation!"
>>> re.sub(r"\s+|\b", '\f', s).split('\f')
['', 'Split', 'along', 'words', ',', 'preserve', 'punctuation', '!']
Where `'\f'` can be replaced by any unused character.
Problem
One particular quirk of the (otherwise quite powerful) `re` module in Python is that `re.split()` will never split a string on a zero-length match, for example if I want to split a string along word boundaries: ``` >>> re.split(r"\s+|\b", "Split along words, preserve punctuation!") ['Split', 'along', 'words,', 'preserve', 'punctuation!'] ``` instead of ``` ['', 'Split', 'along', 'words', ',', 'preserve', 'punctuation', '!'] ``` Why does it have this limitation? Is it by design? Do other regex flavors behave like this?