code: def str_equals(a, b):
      
      al = len(a)
      bl = len(b)
      match = True
      for i in xrange(0, min(al, bl)):
          match &= a[i] == b[i]
      return match
docs: Constant time string equals method - no time leakage
      :param a:
      :param b:
      :return: