试图使用我的小方法,但我得到了以下错误:
class mycls:
def __init__(self):
...
def __enter__(self):
...
def little(self):
...
def __exit__(self, exc_type, exc_val, exc_tb):
...
with mycls() as cl:
cl.little()
with cl:
cl.little()
with cl:
cl.little()
cl.little()
错误:
AttributeError: 'NoneType' object has no attribute 'little'
with
语句不将mycls
的实例本身绑定到cl
,而是将该实例的__enter__
方法的返回值绑定到。当前,mycls.__enter__
返回None
,因此出现观察到的错误。将__enter__
更改为
def __enter__(self):
return self
并且您的代码应该按预期工作。
类似的代码
with foo as bar:
...
(忽略了很多细节(与大致相同
x = foo()
bar = x.__enter__()
...
x.__exit__()
您需要从__enter__
:返回self
class mycls:
def __enter__(self):
return self
def __exit__(self, *_):
pass
def little(self):
pass
with mycls() as cl:
cl.little()
with cl:
cl.little()
with cl:
cl.little()
cl.little()