Misleading message "Right contains one more item"

[sanyassh]

When pytest compares lists of different length and tries to show what the extra items are, it prints incorrect message "Right contains one more item" pointing to the wrong item. At the same time the "Full diff" section correctly indicates extra item. For "Left contains" issue is the same.

Minimal example:

    def test_cmp():
>       assert ['1', '2', '3'] == ['1', '2', '0', '3']
E       AssertionError: assert ['1', '2', '3'] == ['1', '2', '0', '3']
E         
E         At index 2 diff: '3' != '0'
E         Right contains one more item: '3'
E         
E         Full diff:
E           [
E               '1',
E               '2',
E         -     '0',
E               '3',
E           ]

versions:
Ubuntu 22.04.5 LTS
pytest 8.3.3

[The-Compiler]

I think the explanation is correct (even though confusing). Imagine you're looking at pairs of item step by step, basically:

>>> list(itertools.zip_longest(['1', '2', '3'], ['1', '2', '0', '3']))
[('1', '1'), ('2', '2'), ('3', '0'), (None, '3')]

Then indeed you'll see the differences as explained by pytest:

• At index 2, the rhs has a 0 in place of a 3
• The rhs has an additional item, which is 3

Not sure what to do here. Probably pytest would need to be quite clever (possibly too clever) to explain this in human language based on what a diff can show.