深入讲解Python中的上下文管理器和with语句

class MyContextManager:
    def __enter__(self):
        print('Entering the block')
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        print('Exiting the block')

import time
class TimerContextManager:
    def __enter__(self):
        self.start_time = time.time()
    def __exit__(self, exc_type, exc_val, exc_tb):
        end_time = time.time()
        print(f'Time elapsed: {end_time - self.start_time} seconds')
with TimerContextManager():
    # 模拟耗时操作
    time.sleep(2)

from contextlib import contextmanager
@contextmanager
def managed_file(name):
    try:
        f = open(name, 'w')
        yield f
    finally:
        f.close()
with managed_file('hello.txt') as f:
    f.write('Hello, world!')
    f.write('Bye now!')

class AsyncContextManager:
    async def __aenter__(self):
        print('Entering the block')
        return self
    async def __aexit__(self, exc_type, exc_val, exc_tb):
        print('Exiting the block')
async def main():
    async with AsyncContextManager():
        print('Inside the block')
import asyncio
asyncio.run(main())