balanced_parantheses.py

#A small check for balanced parantheses in Python 3
#Added regex as a little extra

import re

any_parantheses = re.compile("[\[({})\]]+")
opening_parantheses = ['[', '(', '{']
closing_parantheses = [']', ')', '}']

def is_balanced(expr):
  stack = []
  n = len(expr)
  for i in range(0, n):
    if(expr[i] in opening_parantheses):
      stack.append(expr[i])
    elif(expr[i] in closing_parantheses):
      matching_paranthesis = opening_parantheses[closing_parantheses.index(expr[i])]
      if(stack.pop() != matching_paranthesis):
        return False

  return True if len(stack) == 0 else False


def main():
  expr = input("Please enter an expression with parantheses ('[','(','{','}',')',']') or 'test' for a fixed test: ")
  if(expr == "test"):
    expr = "({}[](([{()}])))"

  if(not any_parantheses.match(expr)):
    print("No parantheses found!")
  elif(is_balanced(expr)):
    print("%s is balanced!" % expr)
  else:
    print("%s is not balanced!" % expr)

if __name__ == '__main__':
	main()