Typing: Is there a "cast operator"? [RESOLVED]

[Paulo da Silva]

Às 21:36 de 23/10/22, Paulo da Silva escreveu:
> Hello!
> 
> I am in the process of "typing" of some of my scripts.
> Using it should help a lot to avoid some errors.
> But this is new for me and I'm facing some problems.
> 
> Let's I have the following code (please don't look at the program content):
> 
> f=None  # mypy naturally assumes Optional(int) because later, at open, 
> it is assigned an int.
> ..
> if f is None:
>      f=os.open(...
> ..
> if f is not None:
>      os.write(f, ...)
> ..
> if f is not None:
>      os.close(f)
> 
> When I use mypy, it claims
> Argument 1 to "write" has incompatible type "Optional[int]"; expected "int"
> Argument 1 to "close" has incompatible type "Optional[int]"; expected "int"
> 
> How to solve this?
> Is there a way to specify that when calling os.open f is an int only?
And yes there is! Exactly the "cast" operator. A mistype led me to wrong 
search results. I'm sorry.

So, in the above code, we have to do:
os.write(cast(int,f), ...)
and
os.close(cast(int,f), ...)

Regards.
Paulo