feat: add is_pandas_index, is_modin_index, is_cudf_index, is_pandas_like_index utility functions (#1272)

* add is_index method to pandas-like methods

* add test for is_pandas_index, add no cover for other libraries

* add pandas and modin tests

* remove modin from tests

Author: raisadz

docs/api-reference/dependencies.md

@@ -11,15 +11,19 @@
         - get_polars
         - get_pyarrow
         - is_cudf_dataframe
+        - is_cudf_index
         - is_cudf_series
         - is_dask_dataframe
         - is_ibis_table
         - is_into_series
         - is_modin_dataframe
+        - is_modin_index
         - is_modin_series
         - is_numpy_array
         - is_pandas_dataframe
+        - is_pandas_index
         - is_pandas_like_dataframe
+        - is_pandas_like_index
         - is_pandas_like_series
         - is_pandas_series
         - is_polars_dataframe

narwhals/dependencies.py

@@ -98,6 +98,11 @@ def is_pandas_series(ser: Any) -> TypeGuard[pd.Series[Any]]:
     return (pd := get_pandas()) is not None and isinstance(ser, pd.Series)
 
 
+def is_pandas_index(index: Any) -> TypeGuard[pd.Index]:
+    """Check whether `index` is a pandas Index without importing pandas."""
+    return (pd := get_pandas()) is not None and isinstance(index, pd.Index)
+
+
 def is_modin_dataframe(df: Any) -> TypeGuard[mpd.DataFrame]:
     """Check whether `df` is a modin DataFrame without importing modin."""
     return (mpd := get_modin()) is not None and isinstance(df, mpd.DataFrame)
@@ -108,6 +113,13 @@ def is_modin_series(ser: Any) -> TypeGuard[mpd.Series]:
     return (mpd := get_modin()) is not None and isinstance(ser, mpd.Series)
 
 
+def is_modin_index(index: Any) -> TypeGuard[mpd.Index]:
+    """Check whether `index` is a modin Index without importing modin."""
+    return (mpd := get_modin()) is not None and isinstance(
+        index, mpd.Index
+    )  # pragma: no cover
+
+
 def is_cudf_dataframe(df: Any) -> TypeGuard[cudf.DataFrame]:
     """Check whether `df` is a cudf DataFrame without importing cudf."""
     return (cudf := get_cudf()) is not None and isinstance(df, cudf.DataFrame)
@@ -118,6 +130,13 @@ def is_cudf_series(ser: Any) -> TypeGuard[cudf.Series[Any]]:
     return (cudf := get_cudf()) is not None and isinstance(ser, cudf.Series)
 
 
+def is_cudf_index(index: Any) -> TypeGuard[cudf.Index]:
+    """Check whether `index` is a cudf Index without importing cudf."""
+    return (cudf := get_cudf()) is not None and isinstance(
+        index, cudf.Index
+    )  # pragma: no cover
+
+
 def is_dask_dataframe(df: Any) -> TypeGuard[dd.DataFrame]:
     """Check whether `df` is a Dask DataFrame without importing Dask."""
     return (dd := get_dask_dataframe()) is not None and isinstance(df, dd.DataFrame)
@@ -174,13 +193,24 @@ def is_pandas_like_dataframe(df: Any) -> bool:
     return is_pandas_dataframe(df) or is_modin_dataframe(df) or is_cudf_dataframe(df)
 
 
-def is_pandas_like_series(arr: Any) -> bool:
+def is_pandas_like_series(ser: Any) -> bool:
     """
-    Check whether `arr` is a pandas-like Series without doing any imports
+    Check whether `ser` is a pandas-like Series without doing any imports
 
     By "pandas-like", we mean: pandas, Modin, cuDF.
     """
-    return is_pandas_series(arr) or is_modin_series(arr) or is_cudf_series(arr)
+    return is_pandas_series(ser) or is_modin_series(ser) or is_cudf_series(ser)
+
+
+def is_pandas_like_index(index: Any) -> bool:
+    """
+    Check whether `index` is a pandas-like Index without doing any imports
+
+    By "pandas-like", we mean: pandas, Modin, cuDF.
+    """
+    return (
+        is_pandas_index(index) or is_modin_index(index) or is_cudf_index(index)
+    )  # pragma: no cover
 
 
 def is_into_series(native_series: IntoSeries) -> bool:

tests/dependencies/is_pandas_index_test.py

@@ -0,0 +1,12 @@
+from __future__ import annotations
+
+import pandas as pd
+
+from narwhals.dependencies import is_pandas_index
+
+
+def test_is_pandas_index() -> None:
+    data = [1, 2]
+    s_pd = pd.Series(data)
+    assert is_pandas_index(s_pd.index)
+    assert not is_pandas_index(data)