Trailing empty string after re.split()

Question

I have two strings where I want to isolate sequences of digits from everything else.

For example:

import re
s = 'abc123abc'
print(re.split('(\d+)', s))
s = 'abc123abc123'
print(re.split('(\d+)', s))

The output looks like this:

['abc', '123', 'abc']
['abc', '123', 'abc', '123', '']

Note that in the second case, there's a trailing empty string.

Obviously I can test for that and remove it if necessary but it seems cumbersome and I wondered if the RE can be improved to account for this scenario.

Answer 1

This has to do with the implementation of re.split() itself: you can't change it. When the function splits, it doesn't check anything that comes after the capture group, so it can't choose for you to either keep or discard the empty string that is left after splitting. It just splits there and leaves the rest of the string (which can be empty) to the next cycle.

If you don't want that empty string, you can get rid of it in various ways before collecting the results into a list. user1740577's is one example, but personally I prefer a list comprehension, since it's more idiomatic for simple filter/map operations:

parts = [part for part in re.split('(\d+)', s) if part]

I recommend against checking and getting rid of the element after the list has already been created, because it involves more operations and allocations.

Answer 2

You can use filter and don't return this empty string like below:

>>> s = 'abc123abc123'
>>> re.split('(\d+)', s)
['abc', '123', 'abc', '123', '']

>>> list(filter(None,re.split('(\d+)', s)))
['abc', '123', 'abc', '123']

By thanks @chepner you can generate list comprehension like below:

>>> [x for x in re.split('(\d+)', s) if x]
['abc', '123', 'abc', '123']

If maybe you have symbols or other you need split:

>>> s = '&^%123abc123$#@123'
>>> list(filter(None,re.split('(\d+)', s)))
['&^%', '123', 'abc', '123', '$#@', '123']