可选的类型注释.检查是否为无后使用值? [英] Optional type annotation. Using value after checking if is None?

问题描述

我正在用 python 编写一些带有类型注释的代码.我有 Optional 类型的问题.例如对于这样的代码:

I was writing some code with type annotations in python. I have problem with Optional type. For example for a code like this:

maybe_number : Optional[int] =  ... # definition
if maybe_number == None:
    ...
else:
    # I know its int because i checked, but it is a typechecking error
    number : int = maybe_number 
    ...

出现错误:

Incompatible types in assignment (expression has type "Optional[int]", variable has type "int")

如何在python中表示我知道某个分支中具有联合或可选类型的实际值类型.我需要以特定方式检查类型吗?

How can I express in python that I know actual type of value with Union or Optional type in certain branch. Do I need to check type in a specific way?

推荐答案

Equality 实际上并没有告诉你很多关于对象类型的信息，因为这两个对象可能有 __eq__ 方法，允许它们相同但不同，甚至不相关的类型.您可以通过使用身份比较来检查 maybe_number is 值是否为 None:

Equality doesn't actually tell you much about an objects type, because the two objects could have __eq__ methods that allow them to be equal but of different, even unrelated, types. You can check if maybe_number is the value None by using identity comparison:

if maybe_number is None:
    ...
else:
    number : int = maybe_number

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