A typing question

[Thomas Passin]

On 10/29/2022 1:45 PM, Paulo da Silva wrote:
> Hi!
> 
> Consider this simple script ...
> 
> ___________________
> from typing import List, Optional
> 
> class GLOBALS:
>      foos=None
> 
> class Foo:
> 
>      def __init__(self):
>          pass
> 
> class Foos:
>      Foos: List[Foo]=[]
>      # SOME GLOBALS ARE USED HERE in a real script
> 
>      def __init__(self):
>          pass
> 
> GLOBALS.foos: Optional[Foos]=Foos()
> ___________________
> 
> Running mypy on it:
> pt9.py:18: error: Type cannot be declared in assignment to non-self 
> attribute
> pt9.py:18: error: Incompatible types in assignment (expression has type 
> "Foos", variable has type "None")
> Line  18 is last line and pt9.py is the scrip.
> 
> Replacing last line by
> GLOBALS.foos=Foos()
> and running mypy still gives the second error.
> pt9.py:18: error: Incompatible types in assignment (expression has type 
> "Foos", variable has type "None")
> 
> What is the common practice in these cases?
> 
> Thank you.
> 

I don't understand

class Foos:
      Foos: List[Foo]=[]

If "Foos" is supposed to be a class attribute, then it cannot have the 
same name as the class.  Perhaps you meant the class to be named "Foo". 
Then a class attribute of Foos: List[Foo]=[] might barely make sense. 
Even then, remember that each instance of Foo would only know about the 
same (originally empty) list Foos.  Is that really what you want?