(chore): ensure views of anndata produce distinguishable view classes

src/anndata/_core/views.py

@@ -294,64 +294,64 @@ def as_view(obj, view_args):
 
 
 @as_view.register(np.ndarray)
-def as_view_array(array, view_args):
+def as_view_array(array, view_args) -> ArrayView:
     return ArrayView(array, view_args=view_args)
 
 
 @as_view.register(DaskArray)
-def as_view_dask_array(array, view_args):
+def as_view_dask_array(array, view_args) -> DaskArrayView:
     return DaskArrayView(array, view_args=view_args)
 
 
 @as_view.register(pd.DataFrame)
-def as_view_df(df, view_args):
+def as_view_df(df, view_args) -> DataFrameView:
     return DataFrameView(df, view_args=view_args)
 
 
 @as_view.register(sparse.csr_matrix)
-def as_view_csr_matrix(mtx, view_args):
+def as_view_csr_matrix(mtx, view_args) -> SparseCSRMatrixView:
     return SparseCSRMatrixView(mtx, view_args=view_args)
 
 
 @as_view.register(sparse.csc_matrix)
-def as_view_csc_matrix(mtx, view_args):
+def as_view_csc_matrix(mtx, view_args) -> SparseCSCMatrixView:
     return SparseCSCMatrixView(mtx, view_args=view_args)
 
 
 @as_view.register(sparse.csr_array)
-def as_view_csr_array(mtx, view_args):
+def as_view_csr_array(mtx, view_args) -> SparseCSRArrayView:
     return SparseCSRArrayView(mtx, view_args=view_args)
 
 
 @as_view.register(sparse.csc_array)
-def as_view_csc_array(mtx, view_args):
+def as_view_csc_array(mtx, view_args) -> SparseCSCArrayView:
     return SparseCSCArrayView(mtx, view_args=view_args)
 
 
 @as_view.register(dict)
-def as_view_dict(d, view_args):
+def as_view_dict(d, view_args) -> DictView:
     return DictView(d, view_args=view_args)
 
 
 @as_view.register(ZappyArray)
-def as_view_zappy(z, view_args):
+def as_view_zappy(z, view_args) -> ZappyArray:
     # Previous code says ZappyArray works as view,
     # but as far as I can tell they’re immutable.
     return z
 
 
 @as_view.register(CupyArray)
-def as_view_cupy(array, view_args):
+def as_view_cupy(array, view_args) -> CupyArrayView:
     return CupyArrayView(array, view_args=view_args)
 
 
 @as_view.register(CupyCSRMatrix)
-def as_view_cupy_csr(mtx, view_args):
+def as_view_cupy_csr(mtx, view_args) -> CupySparseCSRView:
     return CupySparseCSRView(mtx, view_args=view_args)
 
 
 @as_view.register(CupyCSCMatrix)
-def as_view_cupy_csc(mtx, view_args):
+def as_view_cupy_csc(mtx, view_args) -> CupySparseCSCView:
     return CupySparseCSCView(mtx, view_args=view_args)
 
 
@@ -373,7 +373,7 @@ def _view_args(self):
             to be attached as "behavior". These "behaviors" cannot take any additional parameters (as we do
             for other data types to store `_view_args`). Therefore, we need to store `_view_args` using awkward's
             parameter mechanism. These parameters need to be json-serializable, which is why we can't store
-            ElementRef directly, but need to replace the reference to the parent AnnDataView container with a weak
+            ElementRef directly, but need to replace the reference to the parent AnnData container with a weak
             reference.
             """
             parent_key, attrname, keys = self.layout.parameter(_PARAM_NAME)
@@ -394,7 +394,7 @@ def __copy__(self) -> AwkArray:
             return array
 
     @as_view.register(AwkArray)
-    def as_view_awkarray(array, view_args):
+    def as_view_awkarray(array, view_args) -> AwkwardArrayView:
         parent, attrname, keys = view_args
         parent_key = f"target-{id(parent)}"
         _registry[parent_key] = parent

tests/test_views.py

@@ -3,6 +3,7 @@
 from contextlib import ExitStack
 from copy import deepcopy
 from operator import mul
+from typing import get_type_hints
 
 import joblib
 import numpy as np
@@ -786,6 +787,42 @@ def test_dataframe_view_index_setting():
     assert a2.obs.index.values.tolist() == ["a", "b"]
 
 
+def test_elem_view_class():
+    """
+    Ensure that:
+
+    (a) AnnData views actually produce view classes
+    (b) Produced view classes are subtypes of their original type
+    which then allows distinguishing views from non-views.
+
+    This test tries to then guarantee that `my_adata.is_view and isinstance(my_adata.obsm['my_array'], BaseArrayClass)`
+    tells a user that they are working with a view class of `obsm['my_array']` that inherits from the base class (and has its methods).
+    """
+    orig = gen_adata((10, 10))
+    subset = orig[:8, :8]
+    assert subset.is_view
+    registry = ad._core.views.as_view.registry
+    as_view_funcs = registry.values()
+    base_classes = registry.keys()
+    # Use set membership to ensure the *actual* view class is used
+    view_types = set(
+        get_type_hints(func)["return"]
+        for func in as_view_funcs
+        if "return" in func.__annotations__
+    )
+    base_types = tuple(base_classes)
+    assert type(subset.obs) in view_types
+    assert type(subset.var) in view_types
+    for view_data in (
+        *subset.obsm.values(),
+        *subset.layers.values(),
+        *subset.obsp.values(),
+    ):
+        view_data_type = type(view_data)
+        assert view_data_type in view_types
+        assert isinstance(view_data, base_types)
+
+
 # @pytest.mark.parametrize("dim", ["obs", "var"])
 # @pytest.mark.parametrize(
 #     ("idx", "pat"),