Constant vs variable as index for none-checking List[Optional[...]]

Can you explain to me why there is this difference between using a constant and a variable as index for none-checking here?

from typing import List, Optional

my_list: List[Optional[float]] = []

if my_list[0] is not None:
    result_1: float = my_list[0]        # no error
    result_2: float = my_list[1]        # error: Incompatible types in assignment (expression has type "Optional[float]", variable has type "float")

id_0 = 0
if my_list[id_0] is not None:
    result_3: float = my_list[id_0]     # error: Incompatible types in assignment (expression has type "Optional[float]", variable has type "float")


for i in range(10):
    if my_list[i] is not None:
        a: float = my_list[i]           # error: Incompatible types in assignment (expression has type "Optional[float]", variable has type "float")

• Mypy version used: 0.800 0.941
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: python3.6
• Operating system and version: Ubuntu 18.04 in WSL2 (Windows 11)

L’issue ne mentionne aucun fichier ni test du dépôt. Reproduisez les exemples avec mypy 0.941, puis retracez le comportement du raffinement de type pour les expressions indexées de type List[Optional[float]]. Le travail est terminé lorsque le comportement différent des constantes, des variables et des indices de boucle est expliqué et, s’il est confirmé qu’il s’agit d’un bug, couvert par un regression test approprié.