NoReturn与"void"中的None函数-Python 3.6中的类型注释

问题描述

Python 3.6支持类型注释，例如:

Python 3.6 supports type annotation, like:

def foo() -> int:
    return 42

但是，当一个函数没有返回任何东西时，期望使用什么呢? PEP484 示例大多使用None作为返回类型，但也有typing包中的NoReturn类型.

But what is expected to use when a function hasn't return anything? PEP484 examples mostly use None as a return type, but there is also NoReturn type from typing package.

所以，问题是什么是更可取的，什么是最佳实践:

So, the question is what is preferable to use and what is considered a best practice:

def foo() -> None:
    #do smth

或

from typing import NoReturn

def foo() -> NoReturn:
    #do smth

推荐答案

NoReturn表示函数从不返回值.

NoReturn means the function never returns a value.

函数不会终止或总是引发异常:"键入模块提供特殊类型NoReturn来注释从不正常返回的函数.例如，无条件引发异常的函数.".

from typing import NoReturn

def stop() -> NoReturn:
    raise RuntimeError('no way')

也就是说，x = foo_None()是类型有效的，但是怀疑x = foo_NoReturn()是无效的.

That is, x = foo_None() is type-valid but suspect while x = foo_NoReturn() is invalid.

除了永远不会有可分配的结果外，NoReturn在分支分析中还具有其他含义:foo_NoReturn(); unreachable... 需要NoReturn类型#165'票证中有进一步的讨论.

Besides never having an assignable result, NoReturn also has other implications in branch analysis: foo_NoReturn(); unreachable... There is further discussion in the 'A NoReturn type is needed #165' ticket.

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