regex module shows the same behavior as re module in this case:

  $ python -mtimeit -s "s=' '*20000; import regex as re" "re.search(r'\s+$', s)" # ends with spaces is fast
  10000 loops, best of 3: 201 usec per loop
  $ python -mtimeit -s "s=' '*20000+'non-space'; import regex as re" "re.search(r'\s+$', s)" # ends with a non-space is slow
  10 loops, best of 3: 3.39 sec per loop