Fix .plot error when using positional args with col and row (#11111)

* Ensure plotting returns even with some positional args
* Test that warnings and errors happen
* Don't allow positional args in scatter since they don't work

Author: jsignell

doc/whats-new.rst

@@ -26,13 +26,15 @@ Deprecations
 Bug Fixes
 ~~~~~~~~~
 
+- Fix ``.plot`` error when using positional args with ``col`` and
+  ``row`` (:issue:`11104` :pull:`11111`).
+  By `Julia Signell <https://github.com/jsignell>`_.
 - Slightly amend `Xarray's Zarr Encoding Specification doc <https://docs.xarray.dev/en/latest/internals/zarr-encoding-spec.html>`_ for clarity, and provide a code comment in ``xarray.backends.zarr._get_zarr_dims_and_attrs`` referencing the doc (:issue:`8749` :pull:`11013`).
   By `Ewan Short <https://github.com/eshort0401>`_.
 - Fix silent data corruption when writing dask arrays to sharded Zarr stores.
   Dask chunk boundaries must now align with shard boundaries, not just internal
   Zarr chunk boundaries (:issue:`10831`).
 
-
 Documentation
 ~~~~~~~~~~~~~
 

xarray/plot/dataarray_plot.py

@@ -641,7 +641,7 @@ def step(
 
 def hist(
     darray: DataArray,
-    *args: Any,
+    *,
     figsize: Iterable[float] | None = None,
     size: float | None = None,
     aspect: AspectOptions = None,
@@ -695,8 +695,6 @@ def hist(
         Additional keyword arguments to :py:func:`matplotlib:matplotlib.pyplot.hist`.
 
     """
-    assert len(args) == 0
-
     if darray.ndim == 0 or darray.size == 0:
         # TypeError to be consistent with pandas
         raise TypeError("No numeric data to plot.")
@@ -928,6 +926,7 @@ def newplotfunc(
                 raise ValueError(msg)
             else:
                 warnings.warn(msg, DeprecationWarning, stacklevel=2)
+            del msg
         del args
 
         if hue_style is not None:
@@ -1461,6 +1460,7 @@ def newplotfunc(
                 raise ValueError(msg)
             else:
                 warnings.warn(msg, DeprecationWarning, stacklevel=2)
+            del msg
         del args
 
         # Decide on a default for the colorbar before facetgrids

xarray/plot/dataset_plot.py

@@ -213,6 +213,7 @@ def newplotfunc(
                 raise ValueError(msg)
             else:
                 warnings.warn(msg, DeprecationWarning, stacklevel=2)
+            del msg
         del args
 
         _is_facetgrid = kwargs.pop("_is_facetgrid", False)
@@ -752,7 +753,7 @@ def _temp_dataarray(ds: Dataset, y: Hashable, locals_: dict[str, Any]) -> DataAr
 @overload
 def scatter(  # type: ignore[misc,unused-ignore]  # None is hashable :(
     ds: Dataset,
-    *args: Any,
+    *,
     x: Hashable | None = None,
     y: Hashable | None = None,
     z: Hashable | None = None,
@@ -793,7 +794,7 @@ def scatter(  # type: ignore[misc,unused-ignore]  # None is hashable :(
 @overload
 def scatter(
     ds: Dataset,
-    *args: Any,
+    *,
     x: Hashable | None = None,
     y: Hashable | None = None,
     z: Hashable | None = None,
@@ -834,7 +835,7 @@ def scatter(
 @overload
 def scatter(
     ds: Dataset,
-    *args: Any,
+    *,
     x: Hashable | None = None,
     y: Hashable | None = None,
     z: Hashable | None = None,
@@ -875,7 +876,7 @@ def scatter(
 @_update_doc_to_dataset(dataarray_plot.scatter)
 def scatter(
     ds: Dataset,
-    *args: Any,
+    *,
     x: Hashable | None = None,
     y: Hashable | None = None,
     z: Hashable | None = None,

xarray/tests/test_plot.py

@@ -834,6 +834,14 @@ def test_slice_in_title_single_item_array(self) -> None:
         title = plt.gca().get_title()
         assert "d = [10.009]" == title
 
+    def test_warns_for_few_positional_args(self) -> None:
+        with pytest.warns(DeprecationWarning, match="Using positional arguments"):
+            self.darray.plot.scatter("period")
+
+    def test_raises_for_too_many_positional_args(self) -> None:
+        with pytest.raises(ValueError, match="Using positional arguments"):
+            self.darray.plot.scatter("period", "foo", "bar", "blue", {})
+
 
 class TestPlotStep(PlotTestCase):
     @pytest.fixture(autouse=True)
@@ -1730,6 +1738,19 @@ def test_colormap_error_norm_and_vmin_vmax(self) -> None:
         with pytest.raises(ValueError):
             self.darray.plot(norm=norm, vmax=2)  # type: ignore[call-arg]
 
+    def test_plot_warns_for_2_positional_args(self) -> None:
+        da = xr.DataArray(
+            np.random.randn(2, 6, 6),
+            dims=("time", "x", "y"),
+            coords={"x": np.arange(6), "y": np.arange(6)},
+        )
+        with pytest.warns(DeprecationWarning, match="Using positional arguments"):
+            self.plotfunc(da, "x", "y", col="time")
+
+    def test_plot_raises_too_many_for_positional_args(self) -> None:
+        with pytest.raises(ValueError, match="Using positional arguments"):
+            self.plotmethod("x", "y", (12, 4))
+
 
 @pytest.mark.slow
 class TestContourf(Common2dMixin, PlotTestCase):
@@ -2890,6 +2911,10 @@ def test_bad_args(
                 x=x, y=y, hue=hue, add_legend=add_legend, add_colorbar=add_colorbar
             )
 
+    def test_does_not_allow_positional_args(self) -> None:
+        with pytest.raises(TypeError, match="takes 1 positional argument"):
+            self.ds.plot.scatter("A", "B")
+
     def test_datetime_hue(self) -> None:
         ds2 = self.ds.copy()