keep_attrs for pad (#7267)

* make use of `keep_attrs` in `Variable.pad`

* propagate `keep_attrs`

* resolve the default `keep_attrs` in `Dataset.pad`

* add tests for `Variable.pad`

* add tests for `Dataset.pad` and keep the `Dataset` attrs

* actually pad the variable

* also check that untouched variables are not modified

* add tests for `DataArray.pad`

* update whats-new.rst

* Set True by default

* move the whats-new.rst entry to the dev section

Co-authored-by: Deepak Cherian <dcherian@users.noreply.github.com>
Co-authored-by: Illviljan <14371165+Illviljan@users.noreply.github.com>

doc/whats-new.rst

@@ -36,6 +36,9 @@ Bug fixes
 ~~~~~~~~~
 - Allow numpy-only objects in :py:func:`where` when ``keep_attrs=True`` (:issue:`7362`, :pull:`7364`).
   By `Sam Levang <https://github.com/slevang>`_.
+- add a ``keep_attrs`` parameter to :py:meth:`Dataset.pad`, :py:meth:`DataArray.pad`,
+  and :py:meth:`Variable.pad` (:pull:`7267`).
+  By `Justus Magin <https://github.com/keewis>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/dataarray.py

@@ -5270,6 +5270,7 @@ def pad(
         | None = None,
         end_values: int | tuple[int, int] | Mapping[Any, tuple[int, int]] | None = None,
         reflect_type: PadReflectOptions = None,
+        keep_attrs: bool | None = None,
         **pad_width_kwargs: Any,
     ) -> T_DataArray:
         """Pad this array along one or more dimensions.
@@ -5347,6 +5348,10 @@ def pad(
             default with an unaltered reflection around the edge value. For
             the "odd" style, the extended part of the array is created by
             subtracting the reflected values from two times the edge value.
+        keep_attrs : bool or None, optional
+            If True, the attributes (``attrs``) will be copied from the
+            original object to the new one. If False, the new object
+            will be returned without attributes.
         **pad_width_kwargs
             The keyword arguments form of ``pad_width``.
             One of ``pad_width`` or ``pad_width_kwargs`` must be provided.
@@ -5414,6 +5419,7 @@ def pad(
             constant_values=constant_values,
             end_values=end_values,
             reflect_type=reflect_type,
+            keep_attrs=keep_attrs,
             **pad_width_kwargs,
         )
         return self._from_temp_dataset(ds)

xarray/core/dataset.py

@@ -7939,6 +7939,7 @@ def pad(
         ) = None,
         end_values: int | tuple[int, int] | Mapping[Any, tuple[int, int]] | None = None,
         reflect_type: PadReflectOptions = None,
+        keep_attrs: bool | None = None,
         **pad_width_kwargs: Any,
     ) -> T_Dataset:
         """Pad this dataset along one or more dimensions.
@@ -8016,6 +8017,10 @@ def pad(
             default with an unaltered reflection around the edge value.  For
             the "odd" style, the extended part of the array is created by
             subtracting the reflected values from two times the edge value.
+        keep_attrs : bool or None, optional
+            If True, the attributes (``attrs``) will be copied from the
+            original object to the new one. If False, the new object
+            will be returned without attributes.
         **pad_width_kwargs
             The keyword arguments form of ``pad_width``.
             One of ``pad_width`` or ``pad_width_kwargs`` must be provided.
@@ -8062,6 +8067,9 @@ def pad(
             coord_pad_mode = "constant"
             coord_pad_options = {}
 
+        if keep_attrs is None:
+            keep_attrs = _get_keep_attrs(default=True)
+
         variables = {}
 
         # keep indexes that won't be affected by pad and drop all other indexes
@@ -8084,11 +8092,13 @@ def pad(
                     constant_values=constant_values,
                     end_values=end_values,
                     reflect_type=reflect_type,
+                    keep_attrs=keep_attrs,
                 )
             else:
                 variables[name] = var.pad(
                     pad_width=var_pad_width,
                     mode=coord_pad_mode,
+                    keep_attrs=keep_attrs,
                     **coord_pad_options,  # type: ignore[arg-type]
                 )
                 # reset default index of dimension coordinates
@@ -8099,7 +8109,8 @@ def pad(
                     indexes[name] = index
                     variables[name] = index_vars[name]
 
-        return self._replace_with_new_dims(variables, indexes=indexes)
+        attrs = self._attrs if keep_attrs else None
+        return self._replace_with_new_dims(variables, indexes=indexes, attrs=attrs)
 
     def idxmin(
         self: T_Dataset,

xarray/core/variable.py

@@ -1432,6 +1432,7 @@ def pad(
         | None = None,
         end_values: int | tuple[int, int] | Mapping[Any, tuple[int, int]] | None = None,
         reflect_type: PadReflectOptions = None,
+        keep_attrs: bool | None = None,
         **pad_width_kwargs: Any,
     ):
         """
@@ -1459,6 +1460,10 @@ def pad(
             default with an unaltered reflection around the edge value.  For
             the "odd" style, the extended part of the array is created by
             subtracting the reflected values from two times the edge value.
+        keep_attrs : bool, optional
+            If True, the variable's attributes (`attrs`) will be copied from
+            the original object to the new one.  If False (default), the new
+            object will be returned without attributes.
         **pad_width_kwargs
             One of pad_width or pad_width_kwargs must be provided.
 
@@ -1515,7 +1520,11 @@ def pad(
             **pad_option_kwargs,
         )
 
-        return type(self)(self.dims, array)
+        if keep_attrs is None:
+            keep_attrs = _get_keep_attrs(default=True)
+        attrs = self._attrs if keep_attrs else None
+
+        return type(self)(self.dims, array, attrs=attrs)
 
     def _roll_one_dim(self, dim, count):
         axis = self.get_axis_num(dim)

xarray/tests/test_dataarray.py

@@ -4166,6 +4166,36 @@ def test_pad_reflect(self, mode, reflect_type) -> None:
         assert actual.shape == (7, 4, 9)
         assert_identical(actual, expected)
 
+    @pytest.mark.parametrize(
+        ["keep_attrs", "attrs", "expected"],
+        [
+            pytest.param(None, {"a": 1, "b": 2}, {"a": 1, "b": 2}, id="default"),
+            pytest.param(False, {"a": 1, "b": 2}, {}, id="False"),
+            pytest.param(True, {"a": 1, "b": 2}, {"a": 1, "b": 2}, id="True"),
+        ],
+    )
+    def test_pad_keep_attrs(self, keep_attrs, attrs, expected) -> None:
+        arr = xr.DataArray(
+            [1, 2], dims="x", coords={"c": ("x", [-1, 1], attrs)}, attrs=attrs
+        )
+        expected = xr.DataArray(
+            [0, 1, 2, 0],
+            dims="x",
+            coords={"c": ("x", [np.nan, -1, 1, np.nan], expected)},
+            attrs=expected,
+        )
+
+        keep_attrs_ = "default" if keep_attrs is None else keep_attrs
+
+        with set_options(keep_attrs=keep_attrs_):
+            actual = arr.pad({"x": (1, 1)}, mode="constant", constant_values=0)
+            xr.testing.assert_identical(actual, expected)
+
+        actual = arr.pad(
+            {"x": (1, 1)}, mode="constant", constant_values=0, keep_attrs=keep_attrs
+        )
+        xr.testing.assert_identical(actual, expected)
+
     @pytest.mark.parametrize("parser", ["pandas", "python"])
     @pytest.mark.parametrize(
         "engine", ["python", None, pytest.param("numexpr", marks=[requires_numexpr])]

xarray/tests/test_dataset.py

@@ -6115,6 +6115,40 @@ def test_pad(self) -> None:
         np.testing.assert_equal(padded["var1"].isel(dim2=[0, -1]).data, 42)
         np.testing.assert_equal(padded["dim2"][[0, -1]].data, np.nan)
 
+    @pytest.mark.parametrize(
+        ["keep_attrs", "attrs", "expected"],
+        [
+            pytest.param(None, {"a": 1, "b": 2}, {"a": 1, "b": 2}, id="default"),
+            pytest.param(False, {"a": 1, "b": 2}, {}, id="False"),
+            pytest.param(True, {"a": 1, "b": 2}, {"a": 1, "b": 2}, id="True"),
+        ],
+    )
+    def test_pad_keep_attrs(self, keep_attrs, attrs, expected) -> None:
+        ds = xr.Dataset(
+            {"a": ("x", [1, 2], attrs), "b": ("y", [1, 2], attrs)},
+            coords={"c": ("x", [-1, 1], attrs), "d": ("y", [-1, 1], attrs)},
+            attrs=attrs,
+        )
+        expected = xr.Dataset(
+            {"a": ("x", [0, 1, 2, 0], expected), "b": ("y", [1, 2], attrs)},
+            coords={
+                "c": ("x", [np.nan, -1, 1, np.nan], expected),
+                "d": ("y", [-1, 1], attrs),
+            },
+            attrs=expected,
+        )
+
+        keep_attrs_ = "default" if keep_attrs is None else keep_attrs
+
+        with set_options(keep_attrs=keep_attrs_):
+            actual = ds.pad({"x": (1, 1)}, mode="constant", constant_values=0)
+            xr.testing.assert_identical(actual, expected)
+
+        actual = ds.pad(
+            {"x": (1, 1)}, mode="constant", constant_values=0, keep_attrs=keep_attrs
+        )
+        xr.testing.assert_identical(actual, expected)
+
     def test_astype_attrs(self) -> None:
         data = create_test_data(seed=123)
         data.attrs["foo"] = "bar"

xarray/tests/test_variable.py

@@ -910,6 +910,33 @@ def test_pad_constant_values(self, xr_arg, np_arg):
         )
         assert_array_equal(actual, expected)
 
+    @pytest.mark.parametrize(
+        ["keep_attrs", "attrs", "expected"],
+        [
+            pytest.param(None, {"a": 1, "b": 2}, {"a": 1, "b": 2}, id="default"),
+            pytest.param(False, {"a": 1, "b": 2}, {}, id="False"),
+            pytest.param(True, {"a": 1, "b": 2}, {"a": 1, "b": 2}, id="True"),
+        ],
+    )
+    def test_pad_keep_attrs(self, keep_attrs, attrs, expected):
+        data = np.arange(10, dtype=float)
+        v = self.cls(["x"], data, attrs)
+
+        keep_attrs_ = "default" if keep_attrs is None else keep_attrs
+
+        with set_options(keep_attrs=keep_attrs_):
+            actual = v.pad({"x": (1, 1)}, mode="constant", constant_values=np.nan)
+
+            assert actual.attrs == expected
+
+        actual = v.pad(
+            {"x": (1, 1)},
+            mode="constant",
+            constant_values=np.nan,
+            keep_attrs=keep_attrs,
+        )
+        assert actual.attrs == expected
+
     @pytest.mark.parametrize("d, w", (("x", 3), ("y", 5)))
     def test_rolling_window(self, d, w):
         # Just a working test. See test_nputils for the algorithm validation