return type same as class gives NameError.

[dn]

On 23/10/2023 04.50, Antoon Pardon via Python-list wrote:
> I have the following small module:
> 
> =-=-=-=-=-=-=-=-=-=-=-= 8< =-=-=-=-=-=-=-=-=-=-=-=-=
> 
> from typing import NamedTuple, TypeAlias, Union
> from collections.abc import Sequence
> 
> PNT: TypeAlias = tuple[float, float]
> 
> class Pnt (NamedTuple):
>      x: float
>      y: float
> 
>      def __add__(self, other: PNT) -> Pnt:
>          return Pnt(self[0] + other[0], self[1] + other[1])
> 
> =-=-=-=-=-=-=-=-=-=-=-= >8 =-=-=-=-=-=-=-=-=-=-=-=-=
> 
> But when I import this, I get the following diagnostic:
> 
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
>    File "/home/sisc/projecten/iudex/problem.py", line 10, in <module>
>      class Pnt (NamedTuple):
>    File "/home/sisc/projecten/iudex/problem.py", line 14, in Pnt
>      def __add__(self, other: PNT) -> Pnt:
>                                       ^^^
> NameError: name 'Pnt' is not defined. Did you mean: 'PNT'?
> 
> 
> Can someone explain what I am doing wrong?

What happens when the advice is followed?

Not sure why declare type-alias and then don't use it, but if insist on 
using class-name will be making a "forward-reference" (because class has 
not yet been fully defined) - see 
https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html#forward-references

-- 
Regards,
=dn