Allow quat descriptor attribute to be None

Quaternion/Quaternion.py

@@ -62,7 +62,8 @@
 class QuatDescr:
     """Descriptor for an attribute that is a Quat.
 
-    This allows setting the attribute with any QuatLike value.
+    This allows setting the attribute with any QuatLike value. If not set, the
+    attribute is ``None``.
 
     Examples
     --------
@@ -75,6 +76,9 @@ class QuatDescr:
     >>> obj = MyClass(att=[10, 20, 30])
     >>> obj.att
     <Quat q1=0.26853582 q2=-0.14487813 q3=0.12767944 q4=0.94371436>
+    >>> obj = MyClass()
+    >>> obj.att is None
+    True
     """
 
     def __set_name__(self, owner, name):
@@ -83,10 +87,12 @@ def __set_name__(self, owner, name):
     def __get__(self, obj, type):
         if obj is None:
             return None
-        return getattr(obj, self._name)
+        return getattr(obj, self._name, None)
 
     def __set__(self, obj, value):
-        setattr(obj, self._name, Quat(value))
+        if value is not None:
+            value = Quat(value)
+        setattr(obj, self._name, value)
 
 
 @numba.njit(cache=True)

Quaternion/tests/test_all.py

@@ -715,13 +715,16 @@ def test_quat_mult():
                 assert np.allclose(q01_0, q01_1, rtol=0, atol=1e-10)
 
 
-def test_cxotime_descr():
+def test_quat_descriptor():
     from dataclasses import dataclass
 
     @dataclass
     class MyClass:
         quat: Quat = QuatDescr()
 
+    obj = MyClass()
+    assert obj.quat is None
+
     obj = MyClass(quat=[10, 20, 30])
     assert isinstance(obj.quat, Quat)
     assert obj.quat.ra == 10