Allow __import__ to take None for the fromlist parameter

[Sachaa-Thanasius]

I think it's more accurate, given CPython bytecode often seems to pass None to fromlist instead of an empty tuple.

Rationale

PowerShell 7.5.3
PS C:\Users\Tushaar> py -3.9 -m dis
import abc
^Z
  1           0 LOAD_CONST               0 (0)
              2 LOAD_CONST               1 (None)
              4 IMPORT_NAME              0 (abc)
              6 STORE_NAME               0 (abc)
              8 LOAD_CONST               1 (None)
             10 RETURN_VALUE
PS C:\Users\name> py -3.10 -m dis
import abc
^Z
  1           0 LOAD_CONST               0 (0)
              2 LOAD_CONST               1 (None)
              4 IMPORT_NAME              0 (abc)
              6 STORE_NAME               0 (abc)
              8 LOAD_CONST               1 (None)
             10 RETURN_VALUE
PS C:\Users\name> py -3.11 -m dis
import abc
^Z
  0           0 RESUME                   0

  1           2 LOAD_CONST               0 (0)
              4 LOAD_CONST               1 (None)
              6 IMPORT_NAME              0 (abc)
              8 STORE_NAME               0 (abc)
             10 LOAD_CONST               1 (None)
             12 RETURN_VALUE
PS C:\Users\name> py -3.12 -m dis
import abc
^Z
  0           0 RESUME                   0

  1           2 LOAD_CONST               0 (0)
              4 LOAD_CONST               1 (None)
              6 IMPORT_NAME              0 (abc)
              8 STORE_NAME               0 (abc)
             10 RETURN_CONST             1 (None)
PS C:\Users\name> py -3.13 -m dis
import abc
^Z
  0           RESUME                   0

  1           LOAD_CONST               0 (0)
              LOAD_CONST               1 (None)
              IMPORT_NAME              0 (abc)
              STORE_NAME               0 (abc)
              RETURN_CONST             1 (None)

https://docs.python.org/3/library/dis.html#opcode-IMPORT_NAME

STACK[-1] and STACK[-2] are popped and provide the fromlist and level arguments of __import__().

Ergo, the LOAD_CONST (None) is being passed as the fromlist parameter, and has been passed since at least CPython 3.9 (maybe even earlier). I'm only showing a test via the dis cli and importing a single module, but the result should be replicable in other conditions.

Plus, the implementation of __import__ in importlib only checks truthiness of fromlist before treating it as populated, so None seems like a valid input when looking there too.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉