[Python] Why doesn’t Python 3.12.6 raise ValueError on slice assignment length mismatch?...

I came across unexpected behavior in Python 3.12.6 while performing slice assignment.

Here’s a minimal example:

l3 = [2, 3, 4, 5]
l3[::1] = [1, 3]
print(l3)


Since l3[::1] selects 4 elements ([2, 3, 4, 5]) and [1, 3] only provides 2 replacement values, I expected:

ValueError: attempt to assign sequence of size 2 to extended slice of size 4


Actually, in CPython 3.12.6 on Windows 11, no error is raised, and the output is:

[1, 3]


Has the behavior of slice assignment changed in Python 3.12.6, or is this an unintended bug? If it's a bug, should it be reported on the Python issue tracker?

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