用python封装一个计时器

以下是一个简单的计时器的Python封装：

import time

class Timer:
    def __init__(self):
        self.start_time = None
        self.end_time = None
    
    def start(self):
        self.start_time = time.time()
        print("Timer started.")
    
    def stop(self):
        self.end_time = time.time()
        print("Timer stopped.")
    
    def get_elapsed_time(self):
        if self.start_time is None:
            print("Timer has not been started.")
            return None
        elif self.end_time is None:
            print("Timer has not been stopped.")
            return None
        else:
            elapsed_time = self.end_time - self.start_time
            print("Elapsed time: {:.2f} seconds.".format(elapsed_time))
            return elapsed_time

使用方法：

timer = Timer()
timer.start()
# Code to be timed
timer.stop()
timer.get_elapsed_time()

输出：

Timer started.
Timer stopped.
Elapsed time: 3.14 seconds.