Add QuatDescr descriptor and QuatLike type alias

Quaternion/Quaternion.py

@@ -42,12 +42,51 @@
 
 import operator
 import warnings
+from typing import Annotated, List
 
 import numba
 import numpy as np
+import numpy.typing as npt
 from astropy.utils.shapes import ShapedLikeNDArray
 
-__all__ = ["Quat", "quat_to_equatorial", "quat_mult", "normalize"]
+__all__ = [
+    "Quat",
+    "QuatDescr",
+    "QuatLike",
+    "quat_to_equatorial",
+    "quat_mult",
+    "normalize",
+]
+
+
+class QuatDescr:
+    """Descriptor for an attribute that is a Quat.
+
+    This allows setting the attribute with any QuatLike value.
+
+    Examples
+    --------
+    >>> from dataclasses import dataclass
+    >>> from Quaternion import Quat, QuatDescr
+    >>> @dataclass
+    ... class MyClass:
+    ...     att: Quat = QuatDescr()
+    ...
+    >>> obj = MyClass(att=[10, 20, 30])
+    >>> obj.att
+    <Quat q1=0.26853582 q2=-0.14487813 q3=0.12767944 q4=0.94371436>
+    """
+
+    def __set_name__(self, owner, name):
+        self._name = "_" + name
+
+    def __get__(self, obj, type):
+        if obj is None:
+            return None
+        return getattr(obj, self._name)
+
+    def __set__(self, obj, value):
+        setattr(obj, self._name, Quat(value))
 
 
 @numba.njit(cache=True)
@@ -1074,3 +1113,7 @@ def normalize(array):
         warnings.warn("Normalizing quaternion with zero norm")
 
     return quat
+
+
+# Type alias for a quaternion-like object.
+QuatLike = Quat | Annotated[List[float], 4] | Annotated[List[float], 3] | npt.ArrayLike

Quaternion/tests/test_all.py

@@ -5,7 +5,7 @@
 import numpy as np
 import pytest
 
-from Quaternion import Quat, normalize, quat_mult, quat_to_equatorial
+from Quaternion import Quat, QuatDescr, normalize, quat_mult, quat_to_equatorial
 
 
 def indices(t):
@@ -713,3 +713,23 @@ def test_quat_mult():
                 q01_0 = (q0 * q1).q
                 q01_1 = quat_mult(q0.q, q1.q)
                 assert np.allclose(q01_0, q01_1, rtol=0, atol=1e-10)
+
+
+def test_cxotime_descr():
+    from dataclasses import dataclass
+
+    @dataclass
+    class MyClass:
+        quat: Quat = QuatDescr()
+
+    obj = MyClass(quat=[10, 20, 30])
+    assert isinstance(obj.quat, Quat)
+    assert obj.quat.ra == 10
+    assert obj.quat.dec == 20
+    assert obj.quat.roll == 30
+    assert np.allclose(
+        obj.quat.q,
+        [0.26853582, -0.14487813, 0.12767944, 0.94371436],
+        rtol=0,
+        atol=1e-8,
+    )