如何向工厂方法添加提示? [英] How to add hint to a factory method?

问题描述

我正在寻找一种方法来注释工厂函数的返回类型.

I'm looking for a way to annotate return type of a factory function.

它返回'AlgorithmBase'的随机子节点.

It returns random child of 'AlgorithmBase'.

class AlgorithmFactory:
    _algorithm_types = AlgorithmBase.__subclasses__()

    def select_random_algorithm(self) -> AlgorithmBase:
        # Select random algorithm
        algorithm_class = self._random_generator.choice(AlgorithmFactory._algorithm_types)
        algorithm = algorithm_class()
        return algorithm

我从 mypy 得到错误:

I get error from mypy:

我得到的错误是:

Cannot instantiate abstract class 'AlgorithmBase' with abstract attributes 'get_constraints' and 'satisfy_constraints'

这段代码中没有办法实例化'AlgorithmBase'类，如何让mypy理解呢?

There is no way to instantiate class 'AlgorithmBase' in this code, how to make mypy understand it?

我想避免在返回类型中指定带有Union"的实际子类.有什么建议吗?

I want to avoid specifying actual sub-classes with 'Union' in return type. Any suggestions?

推荐答案

这里的问题不是返回类型，而是_algorithm_types".mypy 无法理解它是什么类型，所以它假设它像返回类型并出错.

The problem here wasn't return type, but '_algorithm_types'. mypy has no way to understand what type it is, so it assumed that it is like return type and got error.

以下代码解决了这个问题:

The following code fix the issue:

_algorithm_types: List[Type[AlgorithmBase]] = AlgorithmBase.__subclasses__()

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