input: Write a python function to check if a string `s` contains matching parentheses (`()`), and return `True` if all parentheses match, otherwise return `False`. If the string is empty, return `True`.
  
  def matching_paren(s):
      stack = []
      for char in s:
          if char == '(':
              stack.append(char)
          elif char == ')':
              if len(stack) == 0:
                  return False 
              stack.pop()
      
      if len(stack) == 0:
          return True
      else:
          return False
  
  assert matching_paren('()') == True
  assert matching_paren('(hello)') == True
  assert matching_paren('(())') == True
  assert matching_paren('(()') == False
  assert matching_paren('(()))') == False
  assert matching_paren('') == True
output: def matching_paren(s):
      stack = []
      for char in s:
          if char == '(':
              stack.append(char)
          elif char == ')':
              if len(stack) == 0:
                  return False 
              stack.pop()
      
      if len(stack) == 0:
          return True
      else:
          return False