1 #!/usr/bin/env python3

     2 

     3 import re

     4 import sys

     5 

     6 # case of catastrophic backtracking in Python

     7 #

     8 # regex: (a*)*b

     9 # strings: aa...a

    10 #

    11 # call with timing as:

    12 #

    13 #   time ./catastrophic.py 20

    14 

    15 # counter n given on the command line

    16 cn = sys.argv[1]

    17 

    18 # calling the matching function

    19 s = ("a" * int(cn))

    20 m = re.match('(a*)*b' , s) 

    21 

    22 print(s)

    23 print(m)