使用 PEP 484 的动态返回类型

问题描述

假设我有一个函数，它将根据字符串输入参数返回一个类，如下所示:

Say I have a function that will return a class based on a string input parameter, like so:

def foo(bar):
    if bar == 'baz':
        return Baz()
    else:
        return Buz()

在这种情况下，Baz 和 Buz 都是 Biz 的子类，但每个都有许多不同的函数，因此声明返回type 作为超类并不是特别有用.假设我不在乎我的 .pyi 文件是否可怕，有什么方法可以让我声明为给定输入返回的子类?

In this case, both Baz and Buz are subclasses of Biz, but each has a number of distinct functions, so declaring the return type as the superclass is not particularly useful. Assuming I don't care if my .pyi file is hideous, is there any way for me to declare what subclass is returned for a given input?

推荐答案

我认为你不能那么具体，你可以做的是声明某些东西返回两种不同的类型，如下所示:

I don't think you can quite that specifically, what you can do though is declare that something returns two different types like so:

from typing import Union

class Bar:
    pass
class Baz:
    pass

def foo(garply : str) -> Union[Bar, Baz]:
    pass

看看这里的文档:https://www.python.org/dev/peps/pep-0484/#union-types

这里有一个合理的简短概述:http://blog.jetbrains.com/pycharm/2015/11/python-3-5-type-hinting-in-pycharm-5/

And a reasonable short overview here:http://blog.jetbrains.com/pycharm/2015/11/python-3-5-type-hinting-in-pycharm-5/

您最好考虑如何避免这种有问题的设计，而不是如何使用类型提示完美地记录它.

You might be better off thinking how to avoid this questionable design rather than how to perfectly document it with type hints.

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