写一个秒表测试台

以下是一个简单的秒表测试台，可以开始、停止和重置秒表，并记录时间：

import time

def start_stopwatch():
    start_time = time.time()
    return start_time

def stop_stopwatch(start_time):
    elapsed_time = time.time() - start_time
    return elapsed_time

def reset_stopwatch():
    return 0

elapsed_time = 0
is_running = False

while True:
    command = input("Enter command (start, stop, reset, quit): ")
    
    if command == "start":
        if not is_running:
            start_time = start_stopwatch()
            is_running = True
            print("Stopwatch started.")
        else:
            print("Stopwatch is already running.")
    
    elif command == "stop":
        if is_running:
            elapsed_time += stop_stopwatch(start_time)
            is_running = False
            print("Stopwatch stopped.")
        else:
            print("Stopwatch is not running.")
    
    elif command == "reset":
        elapsed_time = reset_stopwatch()
        is_running = False
        print("Stopwatch reset.")
    
    elif command == "quit":
        break
    
    else:
        print("Invalid command.")
    
    print("Elapsed time: %.2f seconds" % elapsed_time)