[pytest-dev] fixtures as context managers

[Ronny Pfannschmidt]

Hi all,

how about using proper context managers in all cases

if a class that implements the context manager protocol is marked as 
fixture, it can be used instead


so we would use

@pytest.fixture
@contextlib.contextmanager
def foo(...):
   ...

however the contextlib stuff might be a bit messy to deal with
so a pytest.contextmanager might be necessary

im -1 on the flag

-- Ronny

On 05/09/2013 03:56 PM, holger krekel wrote:
> Hi Bruno, Andreas, all,
>
> yesterday in my in-house course i demonstrated the change.  Somebody
> pointed out rightly that with 2.3.5 you are allowed to do:
>
>      @pytest.fixture
>      def genfix():
>          yield 1
>          yield 2
>
> Which means that when you write a test you can use the fixture as a generator:
>
>      def test_gen(genfix):
>          for x in genfix:
>              # ...
>
> This is probably used by very few people but to be on the safe side,
> we probably should introduce a flag like this:
>
>      @pytest.fixture(ctx=True)  # signal this is a context manager style fixture
>      def fix():
>          yield 1
>
> What do you think?  Any other suggestions for the flag name?
>
> I'd rather not introduce something like @pytest.contextfixture
> because it would be a duplication of the API (scope, params).
> But i am open to be convinced otherwise.
>
> cheers,
> holger
>
>
>
> On Sun, May 05, 2013 at 10:40 -0300, Bruno Oliveira wrote:
>> Very nice! I always thought the "request.addfinalizer" mechanism somewhat
>> cumbersome. :)
>>
>>
>> On Sun, May 5, 2013 at 10:05 AM, holger krekel<holger at merlinux.eu>  wrote:
>>
>>> Hi all,
>>>
>>> after having been asked by Andreas Pelme and Vladimir Keleshev, repeatedly,
>>> i finally tried to allow fixture functions to be context managers like
>>> this:
>>>
>>>      @pytest.fixture
>>>      def myfixture():
>>>          print "setup"
>>>          yield val
>>>          print "teardown"
>>>
>>> With this, you don't need to use "request.addfinalizer" - pytest does
>>> this by detecting your yield.  I checked this into trunk to allow
>>> experimentation - it seems to work fine with scopes and parametrization.
>>> For pytest, it's really just a slightly different "fixture function
>>> calling"
>>> protocol, contained in this commit:
>>>
>>>
>>> https://bitbucket.org/hpk42/pytest/commits/b93ac0cdae02effaa3c136a681cc45bba757fe46
>>>
>>> Note that i don't plan to extend this yield mechanism to parametrization
>>> as that would meanparametrization at test execution time, rather than at
>>> collection time.  It would be both conceptually and implementation wise
>>> hard to do i think.
>>>
>>> The change is committed to trunk, and you can also do:
>>>
>>>      pip install -i http://pypi.testrun.org -U pytest
>>>
>>> to get pytest-2.3.6.dev2 at least.
>>>
>>> feedback welcome, actually without people actively
>>> wanting it, it might be thrown out again ;)
>>>
>>> holger
>>>
>>>
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>>> Pytest-dev at python.org
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>>>
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