Python实现包含min函数的栈

# coding=utf8'''题目：定义栈的数据结构，请在该类型中实现一个能够得到栈的最小元素的min函数。在该栈中，调用min、push及pop的时间复杂度都是O(1)。'''class Stack():  def __init__(self):    self.main_stack = []    # 辅助栈，每次次最小的元素压入辅助栈    self.assist_stack = []    # 记录栈中的最小元素    self._min = None  def min(self):    return self._min  def push(self, data):    self.main_stack.append(data)    if self._min is None:      self._min = data    else:      if data < self._min:        self._min = data    # 将最小的元素压入辅助栈    self.assist_stack.append(self._min)  def pop(self):    if len(self.main_stack) == 0:      raise Exception('no data')    elif len(self.main_stack) == 1:      self.assist_stack.pop()      self._min = None      return self.main_stack.pop()    else:      self.assist_stack.pop()      self._min = self.assist_stack[-1]      return self.main_stack.pop()if __name__ == '__main__':  s = Stack()  s.push(3)  s.push(4)  s.push(2)  s.push(1)  print s.min()  s.pop()  s.pop()  print s.min()  s.pop()  print s.min()  s.pop()  print s.min()  s.pop()