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Improve abc module and builtin function decorators (with ParamSpec) #5682

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Improve abc module and builtin function decorators (with ParamSpec) #5682

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@srittau srittau commented Jun 23, 2021

  • Make classmethod and staticmethod generic over the function.
  • abstractclassmethod and abstractstaticmethod are classes, not
    functions.
  • Remove mypy-specific comments.
@srittau
Improve abc module and builtin function decorators
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* Make classmethod and staticmethod generic over the function.
* abstractclassmethod and abstractstaticmethod are classes, not
  functions.
* Remove mypy-specific comments.
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Remove unused imports
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Add constructors to abstract{class,static}method
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Akuli
Akuli requested changes Jun 23, 2021
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stdlib/builtins.pyi Outdated
def __init__(self, f: Callable[..., Any]) -> None: ...
def __init__(self, f: _FuncT) -> None: ...
def __new__(cls: Type[_T], *args: Any, **kwargs: Any) -> _T: ...
def __get__(self, obj: _T, type: Optional[Type[_T]] = ...) -> Callable[..., Any]: ...
def __get__(self, obj: _T, type: Type[_T] | None = ...) -> _FuncT: ...
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@Akuli Akuli Jun 23, 2021

This doesn't seem right, because the callable returned from __get__ doesn't take the class as a first argument.

>>> class Foo:
...     @classmethod
...     def bar(cls):
...             print("Bar runs:", cls)
... 
>>> Foo.bar()
Bar runs: <class '__main__.Foo'>
>>> Foo.__dict__['bar'].__func__(Foo)
Bar runs: <class '__main__.Foo'>

Here Foo.__dict__['bar'] is the classmethod object, and for Foo.bar, its __get__ method gets called. The result is a bound method, which basically means that it includes the class similarly to partial:

>>> Foo.bar == Foo.__dict__['bar'].__get__(Foo(), None)
True
>>> Foo.bar
<bound method Foo.bar of <class '__main__.Foo'>>

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@Akuli Akuli Jun 23, 2021

Another problem: I think it calls __get__(None, Foo) when looking up Foo.bar, so None should be allowed for the first argument to __get__.

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@srittau srittau Jun 28, 2021

Good catch. I tried to express this using ParamSpec, but I'm not sure this is correct. Also, do you know in what circumstances the owner argument can be None or not set?

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@Akuli Akuli Jun 28, 2021 •
edited

It appears to be a technicality that doesn't really occur in practice: "Python’s own __getattribute__() implementation always passes in both arguments whether they are required or not." Docs

srittau added 3 commits Jun 28, 2021
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Use ParamSpec for classmethod
409aaa1
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Merge branch 'master' into abcmeta
df2f05f
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Fixes
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Fix ParamSpec
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srittau added 2 commits Jun 28, 2021
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Fix abstractclassmethod
8d73ca4
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Fix typo
e0f6ee1
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@srittau srittau commented Jun 28, 2021

It seems that mypy doesn't support Concatenate yet, at least not in callables. Cf. #4827.

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Akuli
Akuli reviewed Jun 28, 2021
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@Akuli Akuli left a comment

The Concatenates look good to me, but I have never actually used Concatenate.

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srittau added 3 commits Jun 28, 2021
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Consistent type var names
ddfd634
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@{static,class}method takes pos-only arguments
06a0ce0
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Annotate self
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@github-actions github-actions bot commented Jun 28, 2021

Diff from mypy_primer, showing the effect of this PR on open source code:

freqtrade (https://github.com/freqtrade/freqtrade.git)
+ freqtrade/data/history/jsondatahandler.py:26: error: Signature of "ohlcv_get_available_data" incompatible with supertype "IDataHandler"
+ freqtrade/data/history/jsondatahandler.py:38: error: Signature of "ohlcv_get_pairs" incompatible with supertype "IDataHandler"
+ freqtrade/data/history/jsondatahandler.py:126: error: Signature of "trades_get_pairs" incompatible with supertype "IDataHandler"
+ freqtrade/data/history/hdf5datahandler.py:25: error: Signature of "ohlcv_get_available_data" incompatible with supertype "IDataHandler"
+ freqtrade/data/history/hdf5datahandler.py:37: error: Signature of "ohlcv_get_pairs" incompatible with supertype "IDataHandler"
+ freqtrade/data/history/hdf5datahandler.py:125: error: Signature of "trades_get_pairs" incompatible with supertype "IDataHandler"

graphql-core (https://github.com/graphql-python/graphql-core.git)
+ src/graphql/execution/execute.py:212: error: Incompatible types in assignment (expression has type "Callable[[Any], bool]", variable has type "Callable[[Arg(Any, 'value')], bool]")

pydantic (https://github.com/samuelcolvin/pydantic.git)
+ pydantic/class_validators.py:57: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:84: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:100: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:107: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:113: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:125: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:135: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/class_validators.py:328: error: Missing type parameters for generic type "classmethod"  [type-arg]
+ pydantic/main.py:953: error: Missing type parameters for generic type "classmethod"  [type-arg]

@srittau srittau mentioned this pull request Jun 28, 2021
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Akuli
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stdlib/builtins.pyi
@@ -109,19 +113,19 @@ class object:
def __dir__(self) -> Iterable[str]: ...
def __init_subclass__(cls) -> None: ...

class staticmethod(object): # Special, only valid as a decorator.
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@Akuli Akuli Jun 28, 2021

Nit: These comments should be deleted. They seem misleading and mypy-specific to me.

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@Akuli Akuli commented Jun 28, 2021

It's starting to LGTM, but I'm concerned about the new errors in freqtrade. They seem to be coming from usual @classmethod usage.

@srittau srittau changed the title Improve abc module and builtin function decorators Improve abc module and builtin function decorators (with ParamSpec) Jun 28, 2021
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