fix(python): raise appropriate error from newly-optimised item on i…

…nvalid (out of bounds) column index (pola-rs#10415)
c-peters · Aug 11, 2023 · b3db64f · b3db64f
1 parent 5249cb1
commit b3db64f
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Showing 3 changed files with 13 additions and 10 deletions.
diff --git a/py-polars/polars/dataframe/frame.py b/py-polars/polars/dataframe/frame.py
@@ -1569,9 +1569,7 @@ def __getitem__(
                 if (col_selection >= 0 and col_selection >= self.width) or (
                     col_selection < 0 and col_selection < -self.width
                 ):
-                    raise ValueError(
-                        f'Column index "{col_selection}" is out of bounds.'
-                    )
+                    raise ValueError(f"column index {col_selection!r} is out of bounds")
                 series = self.to_series(col_selection)
                 return series[row_selection]
 
@@ -1786,13 +1784,16 @@ def item(self, row: int | None = None, column: int | str | None = None) -> Any:
             return self._df.select_at_idx(0).get_idx(0)
 
         elif row is None or column is None:
-            raise ValueError("Cannot call '.item()' with only one of 'row' or 'column'")
+            raise ValueError("cannot call `.item()` with only one of `row` or `column`")
 
-        return (
+        s = (
             self._df.select_at_idx(column)
             if isinstance(column, int)
             else self._df.column(column)
-        ).get_idx(row)
+        )
+        if s is None:
+            raise ValueError(f"column index {column!r} is out of bounds")
+        return s.get_idx(row)
 
     def to_arrow(self) -> pa.Table:
         """

diff --git a/py-polars/polars/functions/lazy.py b/py-polars/polars/functions/lazy.py
@@ -748,7 +748,7 @@ def last(column: str | Series | None = None) -> Expr:
         if column.len() > 0:
             return column[-1]
         else:
-            raise IndexError("The series is empty, so no last value can be returned,")
+            raise IndexError("the series is empty, so no last value can be returned")
     return col(column).last()
 
 

diff --git a/py-polars/tests/unit/dataframe/test_df.py b/py-polars/tests/unit/dataframe/test_df.py
@@ -3253,22 +3253,24 @@ def test_item() -> None:
     assert df.item() == 1
 
     df = pl.DataFrame({"a": [1, 2]})
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match=r".* frame has shape \(2, 1\)"):
         df.item()
 
     assert df.item(0, 0) == 1
     assert df.item(1, "a") == 2
 
     df = pl.DataFrame({"a": [1], "b": [2]})
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match=r".* frame has shape \(1, 2\)"):
         df.item()
 
     assert df.item(0, "a") == 1
     assert df.item(0, "b") == 2
 
     df = pl.DataFrame({})
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match=r".* frame has shape \(0, 0\)"):
         df.item()
+    with pytest.raises(ValueError, match="column index 10 is out of bounds"):
+        df.item(0, 10)
 
 
 @pytest.mark.parametrize(