fichtefoll / resumeback Goto Github PK

Something must have changed with how classmethods function in 3.9.

λ pytest -k test_classmethod
================================================= test session starts =================================================
platform linux -- Python 3.9.5, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /home/fichte/code/resumeback
plugins: xonsh-0.9.27
collected 60 items / 58 deselected / 2 selected

tests/test_descriptors.py F.                                                                                    [100%]

====================================================== FAILURES =======================================================
__________________________________________________ test_classmethod ___________________________________________________

    def test_classmethod():
        ts = State()

        class B:
            @classmethod
            @send_self
            def clsmethod(this, cls, param):
                yield defer(this.next)
                assert cls is B
                ts.run = param

        b = B()
>       wait_until_finished(b.clsmethod(123))

tests/test_descriptors.py:33:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
resumeback/__init__.py:371: in __call__
    gen_wrapper.next()  # Start the first iteration
resumeback/__init__.py:109: in _next
    return self._send(generator)
resumeback/__init__.py:147: in _send
    return generator.send(value)
resumeback/__init__.py:357: in wrapper
    return (yield from self.func(gen_wrapper, *args, **kwargs))
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

this = <class 'tests.test_descriptors.test_classmethod.<locals>.B'>
cls = <resumeback.GeneratorWrapper object at 0x7f68d3808430>, param = 123

    @classmethod
    @send_self
    def clsmethod(this, cls, param):
>       yield defer(this.next)
E       AttributeError: type object 'B' has no attribute 'next'

tests/test_descriptors.py:28: AttributeError
------------------------------------------------ Captured stdout call -------------------------------------------------
<bound method test_classmethod.<locals>.B.clsmethod of <class 'tests.test_descriptors.test_classmethod.<locals>.B'>> (123,)
=============================================== short test summary info ===============================================
FAILED tests/test_descriptors.py::test_classmethod - AttributeError: type object 'B' has no attribute 'next'
===================================== 1 failed, 1 passed, 58 deselected in 0.13s ======================================

At first glance, I did not know what yield do in Python, but after having a hard time studying it, I finally understand the idea. But having calling this = yield and later passing the mysterious this.send as callback, does not seem clear than right away defining some lambda or closure. However, you should ask this to a python beginning which do not know neither closures nor what yield does, because I am already used to lambdas and closures. Or perhaps I am not seeing the big picture because the example is too simple or I am too dumb, therefore in a more complex scenario this could have great advantages. Then you could add also a complex example using closures vs resumeback.

I got that linear order, however I do not see how that can easier than just use closures. My problem is against the declaration of the first this = yield and the second yield function(this.send). If I look both codes:

1. With closure

   def main():
       arbitrary_value = 10
   
       def on_done(number):
           number = str(number)
           print("Result:", number * arbitrary_value)
   
       ask_for_user_input("Please enter a number", on_done)

2. With resumeback

   from resumeback import send_self
   
   @send_self
   def main():
       this = yield  # "this" is now a reference to the just-created generator
       arbitrary_value = 10
   
       # Yield pauses execution until one of the generator methods is called,
       # such as `.send`, which we provide as the callback parameter.
       number = yield ask_for_user_input("Please enter a number", this.send)
       number = str(number)
       print("Result:", number * arbitrary_value)

I can clearly understand when I what is going on with closures. But when looking at those two yield's with resumeback, I do not see it working clearly. Basically, I would say that closures are more intuitive than the this = yied plus the second yield function(this.send) call.

I think it would help, if the first this = yield call could not required, so I can forget about it. Hence, only the second yield call could be done like this:

from resumeback import send_self

@send_self
def main():
    arbitrary_value = 10

    # Yield pauses execution until one of the generator methods is called,
    # such as `.send`, which we provide as the callback parameter.
    number = yield ask_for_user_input("Please enter a number", send_self)
    number = str(number)
    print("Result:", number * arbitrary_value)

Can the this = yield call be embed inside the decorator @send_self and formerly to "send myself" I could just call yield function(send_self)?

I would say that it would look much better than having to remember both to do the first call this = yield and yield function(this.send).

@FichteFoll I could do this:

from resumeback import send_self

@send_self
def main(this):
    # Yield pauses execution until one of the generator methods is called,
    # such as `.send`, which we provide as the callback parameter.
    number = yield ask_for_user_input("Please enter a number", this.send)
    number = str(number)
    print("Result:", number * arbitrary_value)

I'm unsure how I would make the above work for methods though. Gonna need even more magic

I would suggest the this to be a function pointer, so, it can be more straight forward. However, I do not know about other usages of it where could not be pointing to a function directly:

from resumeback import send_self

@send_self
def main(myself):
    arbitrary_value = 10

    # Yield pauses execution until one of the generator methods is called,
    # such as `.send`, which we provide as the callback parameter.
    number = yield ask_for_user_input("Please enter a number", myself)
    number = str(number)
    print("Result:", number * arbitrary_value)

For classmethods, perhaps it could be a cumulative sum of decorators:

from resumeback import send_self

@send_self
@classmethod
def main(myself, cls):
    arbitrary_value = 10

    # Yield pauses execution until one of the generator methods is called,
    # such as `.send`, which we provide as the callback parameter.
    number = yield ask_for_user_input("Please enter a number", myself)
    number = str(number)
    print("Result:", number * arbitrary_value)

But I do not know whether or not you can patch stuff like that in Python.