什麼是上下文管理協議

上下文管理協議其實就是with Foo() as f:類似這種寫法

class Foo:
    def __init__(self,name):
        self.name=name
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        print('exit')
        print(exc_type)
        print(exc_val)
        print(exc_tb)
        return True

with Foo('a.txt') as f:
    print('ok')
print('-----------end----------')

用with這種寫法的最大好處就是不用寫f.close()了。