Add HasConstantsNamespace

src/cosmology/api/_core.py

@@ -5,6 +5,7 @@
 from typing import TYPE_CHECKING, Protocol, TypeVar, runtime_checkable
 
 from cosmology.api._array_api import Array
+from cosmology.api._namespace import HasConstantsNamespace
 
 if TYPE_CHECKING:
     from cosmology.api._constants import CosmologyConstantsNamespace
@@ -18,7 +19,7 @@
 
 
 @runtime_checkable
-class Cosmology(Protocol[Array, InputT]):  # type: ignore[misc]
+class Cosmology(HasConstantsNamespace, Protocol[Array, InputT]):  # type: ignore[misc]
     """Cosmology API Protocol."""
 
     @property

src/cosmology/api/_namespace.py

@@ -19,7 +19,17 @@
 
 
 @runtime_checkable
-class CosmologyNamespace(Protocol):
+class HasConstantsNamespace(Protocol):
+    """Protocol for objects that have a constants module."""
+
+    @property
+    def constants(self) -> CosmologyConstantsNamespace:
+        """The constants namespace for this object."""
+        ...
+
+
+@runtime_checkable
+class CosmologyNamespace(HasConstantsNamespace, Protocol):
     """Runtime-checkable Protocol for the Cosmology API namespace.
 
     Examples
@@ -53,8 +63,3 @@ class CosmologyNamespace(Protocol):
     be a `~cosmology.api.CosmologyConstantsNamespace`, but `isinstance` will not
     check this.
     """
-
-    @property
-    def constants(self) -> CosmologyConstantsNamespace:
-        """The cosmology constants API."""
-        ...