BUG: fix: list as index item does not raise

[Andre-Andreati]

• closes BUG: Index.drop_duplicates() is inconsistent for unhashable values #60925
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/v3.0.0.rst file if fixing a bug or adding a new feature.

Problem:

Index constructor was allowing creation of indexes where one of the index's item is a list (unhashable) while others are not lists.

• If all items are lists - like columns=[ ['a', 'b'], ['b', 'c'], ['b', 'c'] ], it will try to create a MultiIndex. Correct.
• If any item is a list, but NOT all - like the initial example, columns=[ 'a', ['b', 'c'], ['b', 'c'] ], there's no check for this condition, and the creation will follow as if all items, including the lists, are valid column names.

Solution:

Added a check in the Index constructor for this case. Raise ValueError.
Added test to check if is raising correctly.
Changed a test that should raise.

[rhshadrach]

Thanks for the PR!

[rhshadrach]

No non-hashable value should occur here. Instead, can you do this check on arr below, and only in the case it's (a) a NumPy array (not an ExtensionArray) and (b) of object dtype. Use pandas.core.dtypes.inference.is_hashable.

[Andre-Andreati]

Hi, thanks for the review!
OK, will do all the changes.
Just didn't get what you mean by "do this check on arr below", do you mean in the try-except block in line 570? Or inside the sanitize_array definition? Or do the check in the arr resulted from the sanitize_array call?
Sorry for the confusion, newbie here, all those approaches seems OK to me, just asking which one you meant.

pandas/pandas/core/indexes/base.py

Lines 566 to 577 in 1da0d02

	if len(data) and isinstance(data[0], tuple):
	# Ensure we get 1-D array of tuples instead of 2D array.
	data = com.asarray_tuplesafe(data, dtype=_dtype_obj)
	try:
	arr = sanitize_array(data, None, dtype=dtype, copy=copy)
	except ValueError as err:
	if "index must be specified when data is not list-like" in str(err):
	raise cls._raise_scalar_data_error(data) from err
	if "Data must be 1-dimensional" in str(err):
	raise ValueError("Index data must be 1-dimensional") from err
	raise

[rhshadrach]

Can you use GH#60925 throughout.

[rhshadrach]

This looks like it should raise on the first line, is that right? If so, can you remove repr(df).

[rhshadrach]

Suggested change

	- Bug in creating :class:`Index` with one item being a ``list`` among others that aren't (should raise ValueError) (:issue:`60925`)
	- Bug in creating :class:`Index` with some items being a non-hashable; this now raises a ``ValueError`` (:issue:`60925`)