We have the following.

>>> 12 = True
SyntaxError: can't assign to literal

>>> True = False
SyntaxError: can't assign to keyword

>>> ... = False

SyntaxError: can't assign to Ellipsis

We also have (works better in monospaced font)

>>> d[] = True
d[] = True
^
SyntaxError: invalid syntax

Beginners might appreciate having instead as error messages:

SyntaxError: can't assign to literal: 12

SyntaxError: can't assign to keyword: True

SyntaxError: can't assign to literal: ...

Jonathan