fix(python): Raise suitable error when invalid column passed to `get_…

…column_index` (#17868)

py-polars/polars/dataframe/frame.py

@@ -4754,6 +4754,8 @@ def get_column_index(self, name: str) -> int:
         ... )
         >>> df.get_column_index("ham")
         2
+        >>> df.get_column_index("sandwich")  # doctest: +SKIP
+        ColumnNotFoundError: sandwich
         """
         return self._df.get_column_index(name)
 

py-polars/src/dataframe/general.rs

@@ -226,8 +226,11 @@ impl PyDataFrame {
         }
     }
 
-    pub fn get_column_index(&self, name: &str) -> Option<usize> {
-        self.df.get_column_index(name)
+    pub fn get_column_index(&self, name: &str) -> PyResult<usize> {
+        Ok(self
+            .df
+            .try_get_column_index(name)
+            .map_err(PyPolarsErr::from)?)
     }
 
     pub fn get_column(&self, name: &str) -> PyResult<PySeries> {

py-polars/tests/unit/dataframe/test_df.py

@@ -2832,7 +2832,6 @@ def test_from_records_u64_12329() -> None:
 
 def test_negative_slice_12642() -> None:
     df = pl.DataFrame({"x": range(5)})
-
     assert_frame_equal(df.slice(-2, 1), df.tail(2).head(1))
 
 
@@ -2841,3 +2840,13 @@ def test_iter_columns() -> None:
     iter_columns = df.iter_columns()
     assert_series_equal(next(iter_columns), pl.Series("a", [1, 1, 2]))
     assert_series_equal(next(iter_columns), pl.Series("b", [4, 5, 6]))
+
+
+def test_get_column_index() -> None:
+    df = pl.DataFrame({"actual": [1001], "expected": [1000]})
+
+    assert df.get_column_index("actual") == 0
+    assert df.get_column_index("expected") == 1
+
+    with pytest.raises(ColumnNotFoundError, match="missing"):
+        df.get_column_index("missing")