设计一个有getmin功能的栈

#python3.5
class NewStack1:
    def __init__(self):
        self.stackData = []
        self.stackMin = []

    def push(self, newNum):
        self.stackData.append(newNum)
        if len(self.stackMin) == 0 or newNum <= self.getMin():
            self.stackMin.append(newNum)

    def pop(self):
        if len(self.stackData) == 0:
            raise Exception("stack is empty!")
        value = self.stackData.pop()
        if self.getMin() == value:
            self.stackMin.pop()
        return value

    def getMin(self):
        if len(self.stackMin) == 0:
            raise Exception("stack is empty!")
        return self.stackMin[-1]