numpy uses __array__ for casting

avoids infinite loop of __init__, __getitem__, and shape. Found on
8cf07f6113

python/damask/_configmaterial.py

@@ -248,7 +248,7 @@ class ConfigMaterial(Config):
         Examples
         --------
         >>> import damask
-        >>> O = damask.Rotation.from_random(3).as_quaternion()
+        >>> O = damask.Rotation.from_random(3)
         >>> phase = ['Aluminum','Steel','Aluminum']
         >>> m = damask.ConfigMaterial().material_add(constituents={'phase':phase,'O':O},
         ...                                          homogenization='SX')

python/damask/_rotation.py

@@ -125,9 +125,18 @@ class Rotation:
         return np.logical_not(self==other)
 
 
+    def __array__(self):
+        """Initializer for numpy."""
+        return self.quaternion
+
+
+    @property
+    def size(self):
+        return self.quaternion[...,0].size
+
     @property
     def shape(self):
-        return self.quaternion.shape[:-1]
+        return self.quaternion[...,0].shape
 
 
     def __len__(self):

python/tests/test_Rotation.py

@@ -689,6 +689,10 @@ class TestRotation:
         with pytest.raises(TypeError):
             Rotation(np.ones(3))
 
+    def test_to_numpy(self):
+        r = Rotation.from_random(np.random.randint(0,10,4))
+        assert np.all(r.as_quaternion() == np.array(r))
+
     @pytest.mark.parametrize('degrees',[True,False])
     def test_Eulers(self,set_of_rotations,degrees):
         for rot in set_of_rotations:
@@ -804,7 +808,11 @@ class TestRotation:
         r = Rotation.from_random()
         assert r == ~~r
 
-    @pytest.mark.parametrize('shape',[None,1,(1,),(4,2),(1,1,1)])
+    @pytest.mark.parametrize('shape',[1,(1,),(4,2),(1,1,1),tuple(np.random.randint(0,10,4))])
+    def test_size(self,shape):
+        assert Rotation.from_random(shape).size == np.prod(shape)
+
+    @pytest.mark.parametrize('shape',[None,1,(1,),(4,2),(1,1,1),tuple(np.random.randint(0,10,4))])
     def test_shape(self,shape):
         r = Rotation.from_random(shape=shape)
         assert r.shape == (shape if isinstance(shape,tuple) else (shape,) if shape else ())