Assignment expression raises error if updating global variable

[rkompass]

Checks

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• I've searched for existing issues matching this bug, and didn't find any.

Port, board and/or hardware

w600, RP2, others

MicroPython version

MicroPython v1.23.0-preview.362.g3995158d9.dirty on 2024-04-19

Reproduction

a=0; print([(a:=a+1) for b in range(10)])

Expected behaviour

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Observed behaviour

SyntaxError: identifier redefined as global

Additional Information

I saw the discussion on #4908
but there it is about a variable created in the comprehension context being available as global outside.

Here is a variable already present as global.

[Gadgetoid]

Similarly weird case:

CPython 3.12.2:

>>> global a; a=0; print([(a:=a+1) for b in range(10)])
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

MicroPython (UNIX standard):

>>> global a; a=0; print([(a:=a+1) for b in range(10)])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 1, in <listcomp>
NameError: local variable referenced before assignment