it's short, but the filter function call is equialent to [c for c in x if str.isdigit(c)] which has the disadvantage that it will go through the whole word and create an array even if there's only one digit and it can be the first character in the word. If we change the call to filter into this:

next(int(c) for c in x if c.isdigit()) this will create a generator which will in this usage will stop on first digit found...

@acaccia

OK I see now in the 2.7 documentation. My mistake, thanks for the help.

If iterable is a string or a tuple, the result also has that type; otherwise it is always a list.

@CrazyMerlyn:
Oops, didn't thought about it, my bad :p

@acaccia, a solution or spoiler should be marked spoiler even when discussing it on a solution thread.
While someone who hasn't solved this problem can't access the solution, the comment is still visible on the home page.

How can int accept the result from filter? int requires a number or string, and filter returns a list.

TypeError: int() argument must be a string, a bytes-like object or a number, not 'filter'

Test cases are incorrect