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docs: Add note on return type of columns property #3575

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2d332c9
docs: Add note on return type of columns property
FBruzzesi Apr 25, 2026
f126b58
merge main
FBruzzesi Apr 26, 2026
934d15d
expand column_names.md
FBruzzesi Apr 26, 2026
beb053a
Add Note in Schema as well
FBruzzesi Apr 26, 2026
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14 changes: 14 additions & 0 deletions narwhals/dataframe.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1353,6 +1353,13 @@ def collect_schema(self) -> Schema:
def columns(self) -> list[str]:
"""Get column names.

Note:
The pandas-like and dask backends allow non-string column names
(e.g. integers or booleans). While discouraged, this is supported,
so the return type is not guaranteed to be `list[str]`.
Comment on lines +1357 to +1359
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@EdAbati EdAbati Apr 26, 2026

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I think the phrasing looks good!

I tried to find alternatives.

For the 2nd sentence we can use something like:
This is discouraged but supported, so the return type is not guaranteed to be list[str].

Or have it all one sentence:

Non-string column names (e.g. integers or booleans) are discouraged but supported by pandas-like and Dask backends, so the return type is not guaranteed to be list[str].

But again, I think your version looks good :)


See [concepts - column names](../concepts/column_names.md) for details.

Examples:
>>> import pyarrow as pa
>>> import narwhals as nw
Expand Down Expand Up @@ -2638,6 +2645,13 @@ def collect_schema(self) -> Schema:
def columns(self) -> list[str]:
r"""Get column names.

Note:
The pandas-like and dask backends allow non-string column names
(e.g. integers or booleans). While discouraged, this is supported,
so the return type is not guaranteed to be `list[str]`.

See [concepts - column names](../concepts/column_names.md) for details.

Examples:
>>> import duckdb
>>> import narwhals as nw
Expand Down
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