http://silveiraneto.net/?p=4188

parentheses_01.py

#!/usr/bin/env python

counter = 0

def parentheses(symbol='(', depth=0, n=5):
   global counter
   counter += 1
   if(depth<n*2):
      parentheses(symbol+'(', depth+1, n)
      parentheses(symbol+')', depth+1, n)
   elif (depth==n*2):
      print symbol

if __name__=="__main__":
   parentheses()
   print counter