Fwd: A typing question

[dn]

Out of interest, tested snippet in PyCharm, cf native-mypy. It flags the 
original:

     GLOBALS.foos: Optional[Foos]=Foos()

but not the fall-back:

     GLOBALS.foos=Foos()


Must admit, the first query coming to mind was: why is the typing taking 
place at initialisation-time, rather than within the (class) definition? 
At definition time "foos" has already been typed as None by implication!


Solution (below) will not work if the mention of Foos in GLOBALS is a 
forward-reference. Either move GLOBALS to suit, or surround "Foos" with 
quotes.


Also, these days (Python version allowing) importing "List" is 
unnecessary. Instead could use "list".



On 30/10/2022 10.23, Sam Ezeh wrote:
> Do you want the following?
> 
> ```
> from typing import List, Optional
> 
> 
> class GLOBALS:
>      foos: Optional[Foos] = None
> 
> 
> class Foo:
>      def __init__(self):
>          pass
> 
> 
> class Foos:
>      Foos: List[Foo] = []
> 
>      def __init__(self):
>          pass
> 
> 
> GLOBALS.foos = Foos()
> ```
> 
> Kind regards,
> Sam Ezeh
> 
> On Sat, 29 Oct 2022 at 22:13, Paulo da Silva <
> p_d_a_s_i_l_v_a_ns at nonetnoaddress.pt> 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.
>>
>> --
>> https://mail.python.org/mailman/listinfo/python-list
>>

-- 
Regards,
=dn