with语句与__enter__,__exit__

class Foo(object):

    def func(self):
        print("func")
        pass

    def __enter__(self):
        print("enter")
        return Foo()

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("close")

# with语句时调用__enter__()方法，该方法的返回值就是e
with Foo() as e:
    e.func()
# with缩进内容技术时自动调用__exit__()方法
# 打印顺序
# enter
# func
# close