python - typehints -> None 或留空

Question

使用 python 3，可以选择使用类型提示。

我的问题是，如果一个函数返回 None，应该添加它还是留空。

即

def hint(p:str) -> None:
    pass

def no_hint(p:str):
    pass

哪个 PEP 解决了这个问题？

Answer 1

要明确，并且始终为返回 None

的函数包含 -> None

因为否则，对于不带参数的函数，类型检查器会假定您根本没有使用类型提示。例如，def foo(): 是要返回 None，还是只是没有类型提示？

PEP 484 - Type Hints间接解决了这个问题:

Note that the return type of __init__ ought to be annotated with -> None. The reason for this is subtle. If __init__ assumed a return annotation of -> None, would that mean that an argument-less, un-annotated __init__ method should still be type-checked? Rather than leaving this ambiguous or introducing an exception to the exception, we simply say that __init__ ought to have a return annotation; the default behavior is thus the same as for other methods.