--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/catastrophic.py	Fri Nov 24 03:10:23 2017 +0000
@@ -0,0 +1,24 @@
+#!/usr/bin/env python
+import re
+import sys
+
+# case of catastrophic backtracking in Python
+#
+# regex: (a?){n} a{n}
+# strings: aa...
+#
+# call with timing as:
+#
+#   > time ./catastrophic.py 20
+
+# counter n given on the command line
+cn = sys.argv[1]
+
+# constructing the regex
+r1 = '((a?){%s})' % cn
+r2 = 'a{%s}' % cn
+
+# calling the matching function
+m = re.match(r1 + r2 , "a" * int(cn)) 
+
+print m.group(0)