如何在没有元类冲突的情况下将泛型类型与 PyQt 子类一起使用?

2022-01-12 00:00:00 python metaclass pyqt5 pyside2 typing

问题描述

我曾尝试使用 sip 包装器类型的 abc.ABCMeta，它在使用 abc.ABC 进行子类化时效果很好.

I had tried the abc.ABCMeta with sip wrapper type, and it works well when subclass with abc.ABC.

class QABCMeta(wrappertype, ABCMeta):
    pass

class WidgetBase(QWidget, metaclass=QABCMeta):
    ...

class InterfaceWidget(WidgetBase, ABC):
    ...

class MainWidget(InterfaceWidget):
    ...

但它不适用于 typing.Generic.

class QGenericMeta(wrappertype, GenericMeta):
    pass

class WidgetBase(QWidget, Generic[T], metaclass=QGenericMeta):
    ...

class GenericWidget(WidgetBase[float]):
    ...

它提出了:

line 980, in __new__
    self if not origin else origin._gorg)
TypeError: can't apply this __setattr__ to sip.wrappertype object

我希望它像往常一样使用通用子类:

I expected it to use generic subclass as usual:

class TableBase(QTableWidget, Generic[T]):
    @abstractmethod
    def raw_item(self, row: int) -> T:
        ...
    def data(self) -> Iterator[T]:
        yield from (self.raw_item(row) for row in range(self.rowCount()))

class MainTable(TableBase[float]):
    def raw_item(self, row: int) -> float:
        return float(self.item(row, 1).text())  # implementation

table = MainTable()
for data in table.data():
    data: float

但是在没有继承Generic[T]的情况下，data仍然是Any.

But the data is still Any when without inherit Generic[T].

可以用 PEP 560 解决类型检查吗?

Can it solved with PEP 560 to do type checking?

解决方案

嗯，我找到了答案.

由于typing.Generic的元类是abc.ABC，它也应该基于abc.ABCMeta.但这仅适用于 Python 3.7 或更高版本.

Since the metaclass of typing.Generic is abc.ABC, it should based on abc.ABCMeta too. But this is only works with Python 3.7 or above.

然后，只需使用 type(QObject) 而不是 sip.wrappertype:

And then, just use type(QObject) instead of sip.wrappertype:

# -*- coding: utf-8 -*-

from abc import abstractmethod, ABC, ABCMeta
from typing import TypeVar, Generic, Iterator
from PyQt5.QtCore import QObject
from PyQt5.QtWidgets import QTableWidget

QObjectType = type(QObject)
T = TypeVar('T')


class QABCMeta(QObjectType, ABCMeta):
    pass


class BaseWidget(QTableWidget, Generic[T], metaclass=QABCMeta):

    @abstractmethod
    def raw_item(self, row: int) -> T:
        ...

    def data(self) -> Iterator[T]:
        yield from (self.raw_item(row) for row in range(self.rowCount()))


class TestWidget(BaseWidget[float], ABC):  # optional inherit ABC.

    def raw_item(self, row: int) -> float:
        return float(self.item(row, 1).text())


if __name__ == '__main__':
    w = TestWidget()
    for f in w.data():
        pass

此代码适用于PyCharm IDE，变量f的注解为float.

This code is works for PyCharm IDE, the annotation of variable f is float.

把PyQt5改成PySide2也可以！

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