实现上下文管理 with

my_open.py

import contextlib


@contextlib.contextmanager
def my_open(file_name):
    # __enter__
    print('open file: ', file_name, 'in_enter')
    file_handler = open(file_name)

    yield file_handler

    # __exit__
    print('close file:', file_name, 'in_exit')
    file_handler.close()
    return


if __name__ == '__main__':
    with open('hello.txt') as f:
        for line in f:
            print(line)