如何在Python 3.6中使用具有不同值类型的Dict使用静态类型检查? [英] How to use static type checking using Dict with different value types in Python 3.6?

问题描述

尝试在Python代码中使用静态类型，因此mypy可以帮助我解决一些隐藏的错误.使用单个变量非常简单

Trying to use static types in Python code, so mypy can help me with some hidden errors. It's quite simple to use with single variables

real_hour: int = lower_hour + hour_iterator

更难将其与列表和字典一起使用，需要导入其他typing库:

Harder to use it with lists and dictionaries, need to import additional typing library:

from typing import Dict, List
hour_dict: Dict[str, str] = {"test_key": "test_value"}

但是主要的问题-如何将其与具有不同值类型的Dicts结合使用，例如:

But the main problem - how to use it with Dicts with different value types, like:

hour_dict = {"test_key": "test_value", "test_keywords": ["test_1","test_2"]}

如果我不对此类词典使用静态输入-mypy向我显示错误，例如:

If I don't use static typing for such dictionaries - mypy shows me errors, like:

len(hour_dict['test_keywords'])
- Argument 1 to "len" has incompatible type

所以，我的问题是:如何向此类词典添加静态类型? :)

So, my question: how to add static types to such dictionaries? :)

推荐答案

您需要某种类型的Union类型.

You need a Union type, of some sort.

from typing import Dict, List, Union

# simple str values
hour_dict: Dict[str, str] = {"test_key": "test_value"}

# more complex values
hour_dict1: Dict[str, Union[str, List[str]]] = {
    "test_key": "test_value", 
    "test_keywords": ["test_1","test_2"]
}

通常，当您需要此或那个"时，您需要一个Union.在这种情况下，您的选项是str和List[str].

In general, when you need an "either this or that," you need a Union. In this case, your options are str and List[str].

有几种方法可以解决这个问题.例如，您可能想定义类型名称以简化内联类型.

There are several ways to play this out. You might, for example, want to define type names to simplify inline types.

OneOrManyStrings = Union[str, List[str]]

hour_dict2: Dict[str, OneOrManyStrings] = {
    "test_key": "test_value", 
    "test_keywords": ["test_1","test_2"]
}

我可能还建议您出于简单性，并行性和规则性的考虑，即使只有一项，也要使所有dict值纯为List[str].这样，您就可以始终取值的len()，而无需事先进行类型检查或保护条件.但是，这些要点是细微的调整.

I might also advise for simplicity, parallelism, and regularity to make all your dict values pure List[str] even if there's only one item. This would allow you to always take the len() of a value, without prior type checking or guard conditions. But those points are nits and tweaks.

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