import time as t
class MyTimer():
    def __init__(self):
        self.unit=['year','month','day','hour','minute','sec']
        self.prompt='未开始';
        self.lasted=[]
        self.begin=0
        self.end=0
    def __str__(self):
        return self.prompt
    __repr__=__str__
    def __add__(self,other):
        prompt="totle time:"
        result=[]
        for index in range(6):
            result.append(self.lasted[index]+other.lasted[index])
            if result[index]:
                prompt+=(str(result[index])+self.unit[index])
        return prompt
    #start
    def start(self):
        self.begin=t.localtime()
        self.prompt='please stop';
        print('start')
    #end
    def stop(self):
        if not self.begin:
            print('please start')
        else:
            self.end=t.localtime()
            self._calc()
            print('end')
    #inner function calulate runtime
    def _calc(self):
        self.lasted=[]
        self.prompt='runtime:'
        for index in range(6):
            self.lasted.append(self.end[index]-self.begin[index])
            if self.lasted[index]:
                self.prompt+=(str(self.lasted[index])+self.unit[index])
        print(self.prompt)
        self.begin=0
        self.end=0
            

>>> t1=MyTimer()
>>> t1.start()
start
>>> t2.stop()
Traceback (most recent call last):
  File "<pyshell#63>", line 1, in <module>
    t2.stop()
NameError: name 't2' is not defined
>>> t1.stop()
runtime:10sec
end
>>> t2=MyTimer()
>>> t2.start()
start
>>> t2.stop()
runtime:4sec
end
>>> t1+t2
'totle time:14sec'
>>>

有时候会出现负数，以后再改吧……