parameters: (s)
return_statement: return True
docstring: 有效的括号序列
docstring_summary: 有效的括号序列
docstring_tokens: 有效的括号序列
function: def valid_parentheses(s):
      """有效的括号序列"""
      stack = []
      for i in s:
          if i == '(':
              stack.append(i)
          elif i == ')' and len(stack) == 0:
              return False
          else:
              stack.pop()
      return True
function_tokens: def valid_parentheses ( s ) : stack = [ ] for i in s : if i == '(' : stack . append ( i ) elif i == ')' and len ( stack ) == 0 : return False else : stack . pop ( ) return True