From 83de8e96cdcc13074ed35f0108cec34cd2717c62 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Tue, 1 Sep 2020 00:14:59 +0200
Subject: [PATCH 01/11] return None if the wrapped data is not a quantity

---
 pint_xarray/accessors.py            |  2 +-
 pint_xarray/tests/test_accessors.py | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 303aae14..b1f97afa 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -244,7 +244,7 @@ def magnitude(self):
 
     @property
     def units(self):
-        return self.da.data.units
+        return getattr(self.da.data, "units", None)
 
     @units.setter
     def units(self, units):
diff --git a/pint_xarray/tests/test_accessors.py b/pint_xarray/tests/test_accessors.py
index 8867af8a..3003ba43 100644
--- a/pint_xarray/tests/test_accessors.py
+++ b/pint_xarray/tests/test_accessors.py
@@ -123,6 +123,17 @@ def test_roundtrip_data(self, example_unitless_da):
         assert_equal(result, orig)
 
 
+class TestPropertiesDataArray:
+    def test_units_getattr(self, example_quantity_da):
+        da = example_quantity_da
+        assert isinstance(da.pint.units, Unit)
+        assert da.pint.units == unit_registry.m
+
+    def test_unit_getattr_unitless(self, example_unitless_da):
+        da = example_unitless_da
+        assert da.pint.units is None
+
+
 @pytest.fixture()
 def example_unitless_ds():
     users = np.linspace(0, 10, 20)

From 91b7262a9328a77d9d33e3bf7d2dd018b45fd51b Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Tue, 1 Sep 2020 00:16:40 +0200
Subject: [PATCH 02/11] fix the units setattr

---
 pint_xarray/accessors.py            |  6 ++----
 pint_xarray/tests/test_accessors.py | 10 ++++++++++
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index b1f97afa..5b13f282 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -4,7 +4,7 @@
 import pint
 from pint.quantity import Quantity
 from pint.unit import Unit
-from xarray import DataArray, register_dataarray_accessor, register_dataset_accessor
+from xarray import register_dataarray_accessor, register_dataset_accessor
 from xarray.core.npcompat import IS_NEP18_ACTIVE
 
 from . import conversion
@@ -249,9 +249,7 @@ def units(self):
     @units.setter
     def units(self, units):
         quantity = conversion.array_attach_units(self.da.data, units)
-        self.da = DataArray(
-            dim=self.da.dims, data=quantity, coords=self.da.coords, attrs=self.da.attrs
-        )
+        self.da.data = quantity
 
     @property
     def dimensionality(self):
diff --git a/pint_xarray/tests/test_accessors.py b/pint_xarray/tests/test_accessors.py
index 3003ba43..55ef3615 100644
--- a/pint_xarray/tests/test_accessors.py
+++ b/pint_xarray/tests/test_accessors.py
@@ -129,10 +129,20 @@ def test_units_getattr(self, example_quantity_da):
         assert isinstance(da.pint.units, Unit)
         assert da.pint.units == unit_registry.m
 
+    def test_units_setattr(self, example_quantity_da):
+        da = example_quantity_da
+        with pytest.raises(ValueError):
+            da.pint.units = "s"
+
     def test_unit_getattr_unitless(self, example_unitless_da):
         da = example_unitless_da
         assert da.pint.units is None
 
+    def test_unit_setattr_unitless(self, example_unitless_da):
+        da = example_unitless_da
+        da.pint.units = unit_registry.s
+        assert da.pint.units == unit_registry.s
+
 
 @pytest.fixture()
 def example_unitless_ds():

From 3ba112ed2647555c2727659a7b6ba5f60ff21e19 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Tue, 1 Sep 2020 00:26:59 +0200
Subject: [PATCH 03/11] add docstrings to the units and dimensionality
 properties

---
 pint_xarray/accessors.py | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 5b13f282..71b46ee9 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -244,15 +244,39 @@ def magnitude(self):
 
     @property
     def units(self):
+        """get the units of the wrapped data
+
+        Returns
+        -------
+        units : pint.Unit or None
+            the units of the wrapped data. If it is not a quantity, the units
+            are :py:obj:`None`.
+        """
         return getattr(self.da.data, "units", None)
 
     @units.setter
     def units(self, units):
+        """set the units of the wrapped data in-place
+
+        Raises
+        ------
+        ValueError
+            If the data already is a quantity, or the units are not a
+            :py:class:`pint.Unit` instance.
+        """
         quantity = conversion.array_attach_units(self.da.data, units)
         self.da.data = quantity
 
     @property
     def dimensionality(self):
+        """get the dimensionality of the data
+
+        Returns
+        -------
+        dimensionality : str or None
+            The dimensionality of the data. If it is not a quantity, the
+            dimensionality is :py:obj:`None`.
+        """
         return self.da.data.dimensionality
 
     @property

From 84932703c2494cb5309b431874e579ed0d7ab913 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Tue, 1 Sep 2020 00:27:29 +0200
Subject: [PATCH 04/11] return a dimensionality of None for non-quantities

---
 pint_xarray/accessors.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 71b46ee9..cce29619 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -277,7 +277,7 @@ def dimensionality(self):
             The dimensionality of the data. If it is not a quantity, the
             dimensionality is :py:obj:`None`.
         """
-        return self.da.data.dimensionality
+        return getattr(self.da.data, "dimensionality", None)
 
     @property
     def registry(self):

From 7ace89aa6779842f9b1fbd7c6a337f6f14f9e16b Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Tue, 1 Sep 2020 00:39:55 +0200
Subject: [PATCH 05/11] fix the magnitude property

---
 pint_xarray/accessors.py            |  7 ++++++-
 pint_xarray/tests/test_accessors.py | 14 ++++++++++++--
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index cce29619..1bde4168 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -240,7 +240,12 @@ def dequantify(self):
 
     @property
     def magnitude(self):
-        return self.da.data.magnitude
+        """get the magnitude of the wrapped data
+
+        If not a quantity, will return the data itself.
+        """
+        data = self.da.data
+        return getattr(data, "magnitude", data)
 
     @property
     def units(self):
diff --git a/pint_xarray/tests/test_accessors.py b/pint_xarray/tests/test_accessors.py
index 55ef3615..4a41a04a 100644
--- a/pint_xarray/tests/test_accessors.py
+++ b/pint_xarray/tests/test_accessors.py
@@ -124,10 +124,20 @@ def test_roundtrip_data(self, example_unitless_da):
 
 
 class TestPropertiesDataArray:
+    def test_magnitude_getattr(self, example_quantity_da):
+        da = example_quantity_da
+        actual = da.pint.magnitude
+        assert not isinstance(actual, Quantity)
+
+    def test_magnitude_getattr_unitless(self, example_unitless_da):
+        da = example_unitless_da
+        xr.testing.assert_duckarray_equal(da.pint.magnitude, da.data)
+
     def test_units_getattr(self, example_quantity_da):
         da = example_quantity_da
-        assert isinstance(da.pint.units, Unit)
-        assert da.pint.units == unit_registry.m
+        actual = da.pint.units
+        assert isinstance(actual, Unit)
+        assert actual == unit_registry.m
 
     def test_units_setattr(self, example_quantity_da):
         da = example_quantity_da

From 79a1b082c9b43d985a1c74d4362cee914e68aa8c Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Tue, 1 Sep 2020 00:41:32 +0200
Subject: [PATCH 06/11] update whats-new.rst

---
 docs/whats-new.rst | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/docs/whats-new.rst b/docs/whats-new.rst
index 4863d6a6..8c219a08 100644
--- a/docs/whats-new.rst
+++ b/docs/whats-new.rst
@@ -9,4 +9,7 @@ What's new
 - rewrite :py:meth:`DataArray.pint.quantify`,
   :py:meth:`Dataset.pint.quantify`, :py:meth:`DataArray.pint.dequantify` and
   :py:meth:`Dataset.pint.dequantify` (:pull:`17`)
-- expose :py:func:`pint_xarray.testing.assert_units_equal` as public API (:pull:`24`)
\ No newline at end of file
+- expose :py:func:`pint_xarray.testing.assert_units_equal` as public API (:pull:`24`)
+- fix the :py:attr:`DataArray.pint.units`, :py:attr:`DataArray.pint.magnitude`
+  and :py:attr:`DataArray.pint.dimensionality` properties and add docstrings for
+  all three. (:pull:`31`)

From 7dc0fed8240cae698537fa92087e61b5b322c4f7 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Fri, 4 Sep 2020 14:42:17 +0200
Subject: [PATCH 07/11] shorten the property docstrings

---
 pint_xarray/accessors.py | 31 +++----------------------------
 1 file changed, 3 insertions(+), 28 deletions(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 3086d526..681b4914 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -230,48 +230,23 @@ def dequantify(self):
 
     @property
     def magnitude(self):
-        """get the magnitude of the wrapped data
-
-        If not a quantity, will return the data itself.
-        """
+        """the magnitude of the data or the data itself if not a quantity."""
         data = self.da.data
         return getattr(data, "magnitude", data)
 
     @property
     def units(self):
-        """get the units of the wrapped data
-
-        Returns
-        -------
-        units : pint.Unit or None
-            the units of the wrapped data. If it is not a quantity, the units
-            are :py:obj:`None`.
-        """
+        """the units of the data or :py:obj:`None` if not a quantity."""
         return getattr(self.da.data, "units", None)
 
     @units.setter
     def units(self, units):
-        """set the units of the wrapped data in-place
-
-        Raises
-        ------
-        ValueError
-            If the data already is a quantity, or the units are not a
-            :py:class:`pint.Unit` instance.
-        """
         quantity = conversion.array_attach_units(self.da.data, units)
         self.da.data = quantity
 
     @property
     def dimensionality(self):
-        """get the dimensionality of the data
-
-        Returns
-        -------
-        dimensionality : str or None
-            The dimensionality of the data. If it is not a quantity, the
-            dimensionality is :py:obj:`None`.
-        """
+        """get the dimensionality of the data or :py:obj:`None` if not a quantity."""
         return getattr(self.da.data, "dimensionality", None)
 
     @property

From db1b8c8cc2a12704bb170db0821816617e3ae5e1 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Fri, 4 Sep 2020 14:50:07 +0200
Subject: [PATCH 08/11] fix the name of the unitless tests

---
 pint_xarray/tests/test_accessors.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pint_xarray/tests/test_accessors.py b/pint_xarray/tests/test_accessors.py
index 4a41a04a..685b0e34 100644
--- a/pint_xarray/tests/test_accessors.py
+++ b/pint_xarray/tests/test_accessors.py
@@ -144,11 +144,11 @@ def test_units_setattr(self, example_quantity_da):
         with pytest.raises(ValueError):
             da.pint.units = "s"
 
-    def test_unit_getattr_unitless(self, example_unitless_da):
+    def test_units_getattr_unitless(self, example_unitless_da):
         da = example_unitless_da
         assert da.pint.units is None
 
-    def test_unit_setattr_unitless(self, example_unitless_da):
+    def test_units_setattr_unitless(self, example_unitless_da):
         da = example_unitless_da
         da.pint.units = unit_registry.s
         assert da.pint.units == unit_registry.s

From 8af972494cac6d24e0758a83ce9454ef13ee54da Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Fri, 4 Sep 2020 14:51:51 +0200
Subject: [PATCH 09/11] mention that units can only be set if the data is not a
 quantity

---
 pint_xarray/accessors.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 681b4914..8b13f753 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -236,7 +236,10 @@ def magnitude(self):
 
     @property
     def units(self):
-        """the units of the data or :py:obj:`None` if not a quantity."""
+        """the units of the data or :py:obj:`None` if not a quantity.
+
+        The units can only be set if the data is not already a quantity.
+        """
         return getattr(self.da.data, "units", None)
 
     @units.setter

From 6bdfd00b78347e935a17275291c169b914eae659 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Fri, 4 Sep 2020 16:52:18 +0200
Subject: [PATCH 10/11] reword the docstring dealing with setting the units

---
 pint_xarray/accessors.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 8b13f753..8a6dfc6f 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -238,7 +238,7 @@ def magnitude(self):
     def units(self):
         """the units of the data or :py:obj:`None` if not a quantity.
 
-        The units can only be set if the data is not already a quantity.
+        Setting the units is possible, but only if the data is not already a quantity.
         """
         return getattr(self.da.data, "units", None)
 

From ae0ce7f254bab2d62f760f20b56badffc8b33f91 Mon Sep 17 00:00:00 2001
From: Keewis <keewis@posteo.de>
Date: Sat, 12 Sep 2020 13:04:46 +0200
Subject: [PATCH 11/11] don't assign a name to the constructed quantity

---
 pint_xarray/accessors.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pint_xarray/accessors.py b/pint_xarray/accessors.py
index 8a6dfc6f..fa97aac7 100644
--- a/pint_xarray/accessors.py
+++ b/pint_xarray/accessors.py
@@ -244,8 +244,7 @@ def units(self):
 
     @units.setter
     def units(self, units):
-        quantity = conversion.array_attach_units(self.da.data, units)
-        self.da.data = quantity
+        self.da.data = conversion.array_attach_units(self.da.data, units)
 
     @property
     def dimensionality(self):