Copilot commented on code in PR #46884:
URL: https://github.com/apache/arrow/pull/46884#discussion_r3298718286
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python/pyarrow/pandas_compat.py:
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@@ -378,7 +378,10 @@ def _index_level_name(index, i, column_names):
if index.name is not None and index.name not in column_names:
return _column_name_to_strings(index.name)
else:
- return f'__index_level_{i:d}__'
+ j = i
+ while f'__index_level_{j:d}__' in column_names:
+ j += 1
+ return f'__index_level_{j:d}__'
Review Comment:
Bumping the generated index column name changes the meaning of the numeric
suffix (it no longer matches the index level position). Later in this module,
`_get_index_level()` assumes that any `__index_level_{n}__` name maps to
`df.index.get_level_values(n)`. With this change, a dataframe that already has
`__index_level_0__` will generate `__index_level_1__` for the first unnamed
index level, but `_get_index_level(df, '__index_level_1__')` would incorrectly
select level 1 (or raise for a single-level index) when a user passes an
explicit schema. Consider updating `_get_index_level()` to resolve generated
index names using the same collision-avoidance logic as `_index_level_name`
(based on `df.columns` and already-assigned index names), so schema-based
conversions keep working.
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