With class as contextmanager

Tue Jan 24 18:25:25 EST 2017

On 01/24/2017 02:35 PM, Ethan Furman wrote:
> On 01/24/2017 01:31 PM, This Wiederkehr wrote:

>> having a class definition:
>>>> class Test():
>>>> @classmethod
>> def __enter__(cls):
>> pass
>>>> @classmethod
>> def __exit__(cls, exception_type, execption_value, callback):
>> pass
>>>> now using this as a contextmanager does not work, even though Test is an
>> object and has the two required methods __enter__ and __exit__.
>> It is not working because you are trying to use the class itself, and not it's instances, as a context manager (which also means you don't need classmethod):
>> Wrong:
>> with Test:
>> Correct:
>> with Test():
>>> I am asking because I'd like to implement the clean up behaviour for
>> multiple instances directly into the class:
>>>> with Test:
>> testinstance1 = Test()
>> testinstance2 = Test()
>> # on context exit Test.__exit__ should take care on cleaning up
>> testinstance1 and testinstance2.
>> You might be able to make this work with a custom type (aka using a custom metaclass) -- but that could be a bunch of work.

Okay, here's the easy part:
--- 8< ----------------------------
class TestType(type):
 def __enter__(cls):
 pass
 def __exit__(cls, *args):
 pass
class Test(metaclass=TestType):
 pass
with Test:
 print('worked!')
--- 8< ----------------------------
Let us know how it turns out.
--
~Ethan~