fix remaining case for DataFrame raising an error if copy could not be avoided

Author: jorisvandenbossche

pandas/core/generic.py

@@ -2014,6 +2014,12 @@ def empty(self) -> bool:
     def __array__(
         self, dtype: npt.DTypeLike | None = None, copy: bool | None = None
     ) -> np.ndarray:
+        if copy is False and not self._mgr.is_single_block and not self.empty:
+            # check this manually, otherwise ._values will already return a copy
+            # and np.array(values, copy=False) will not raise an error
+            raise ValueError(
+                "Unable to avoid copy while creating an array as requested."
+            )
         values = self._values
         if copy is None:
             # Note: branch avoids `copy=None` for NumPy 1.x support

pandas/tests/copy_view/test_array.py

@@ -138,6 +138,9 @@ def test_dataframe_multiple_numpy_dtypes():
     assert not np.shares_memory(arr, get_array(df, "a"))
     assert arr.flags.writeable is True
 
+    with pytest.raises(ValueError, match="Unable to avoid copy while creating"):
+        arr = np.array(df, copy=False)
+
 
 def test_values_is_ea():
     df = DataFrame({"a": date_range("2012-01-01", periods=3)})