bpo-32380: Create functools.singledispatchmethod #6306
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functools.singledispatch interacts poorly with methods and descriptors, thus functools.singledispatchmethod is created to handles these.
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Hm, I'm not sure what is going on with the unexpected indent here. It seems valid. |
| @@ -2147,6 +2147,73 @@ def __eq__(self, other): | |||
| return self.arg == other | |||
| self.assertEqual(i("str"), "str") | |||
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| def test_method_register(self): | |||
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I don't see tests that show that registration of arbitrary callables from outside of the class definition also works.
Something like:
class C:
@singledispatchmethod
def g(self, arg):
...
@C.g.register(int)
def _(self, arg):
...
Doc/library/functools.rst
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| raise NotImplementedError("Cannot negate a") | ||
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| @neg.register(int): | ||
| def _(self, arg): |
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Please document using type annotations as the default way to register types, just like the singledispatch documentation in 3.7+ does.
Lib/functools.py
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| def __init__(self, func): | ||
| if not callable(func) and not hasattr(func, "__get__"): | ||
| raise TypeError("{!r} is not callable or a descriptor" | ||
| .format(func)) |
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nit: this formatting is ugly. Consider:
raise TypeError(
f"{func!r} is not callable or a descriptor"
)
Might even fit in a single line with the f-string.
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A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated. Once you have made the requested changes, please leave a comment on this pull request containing the phrase |
Doc/library/functools.rst
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| like :func:`singledispatch` except that it is designed to be used as a | ||
| method definition rather than being directly callable. | ||
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| :class:`singledispatchmethod` can be used as follows: |
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The unexpected indent is likely because you didn't use double colon (::) here. But I don't know if the empty line doesn't denote an end of the code block in RST. Look for other examples where stuff like this is used in the docs, they will probably hint at a good solution.
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I have made the requested changes; please review again Thanks for the review Łukasz! |
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Thanks for making the requested changes! @ambv: please review the changes made to this pull request. |
Doc/library/functools.rst
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| @@ -383,6 +383,28 @@ The :mod:`functools` module defines the following functions: | |||
| The :func:`register` attribute supports using type annotations. | |||
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| .. class:: singledispatchmethod(func) | |||
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| Return a new :class:`singledispatchmethod` descriptor which behaves | |||
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While this is implemented as a class, I'd suggest borrowing the markup and introductory text from singledispatch and reusing an adjusted version of that text here - from an end user's perspective, the important point is that they can use singledispatchmethod to decorate a method definition and have it dispatch on the first non-self argument.
| @neg.register | ||
| def _(self, arg: bool): | ||
| return not arg | ||
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Having an example stacked with @classmethod would be good here. It's unfortunate that the order of application will need to be different from that when stacking @abstractmethod (see https://docs.python.org/3/library/abc.html#abc.abstractmethod), but we need "register" to be accessible on the resulting descriptor. So something like:
class Negator:
@singledispatchmethod
@classmethod
def neg(cls, arg):
...
Given the @classmethod example, you can then note that the same principle applies for @staticmethod and other decorators - to be useful, @singledispatchmethod typically needs to be the outermost decorator so that the register method is accessible.
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@ncoghlan thanks for the suggestions! I amended the docs as you asked. |
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This is almost there. Two remaining requests:
- in the Negator example in the docs, use cls, not self
- in the tests, use registered implementations which actually use the relevant cls or self to prove they bind correctly; especially in the arbitrary callable case.
Done! Let me know if you have further feedback. |
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I'll wait a few days before merging in case @rhettinger has any input. |
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What is the status here? This seems ready to be merged. (Or maybe it should also support annotations like |
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@ilevkivskyi waiting on naming approval. Also, It does support annotations see https://github.com/python/cpython/pull/6306/files#diff-09cc1e5ad87c6bd130e5b417193ed883R2251 |
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@ambv: Please replace |
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Thanks! ✨ 🍰 ✨ |
I finally found time to follow up after #4987. In review: functools.singledispatch interacts poorly with methods and descriptors, thus I created functools.singledispatchmethod to handles these.
This implementation is based on that of
functools.partialmethod.https://bugs.python.org/issue32380