force HasState Protocol instead

src/pyhf/tensor/manager.py

@@ -5,26 +5,23 @@
 from pyhf import exceptions
 from pyhf import events
 from pyhf.optimize import OptimizerRetriever
-from pyhf.typing import TensorBackend, Optimizer, TypedDict
-from types import ModuleType
-
-_default_backend: TensorBackend = BackendRetriever.numpy_backend()
-_default_optimizer: Optimizer = OptimizerRetriever.scipy_optimizer()  # type: ignore[no-untyped-call]
+from pyhf.typing import TensorBackend, Optimizer, TypedDict, Protocol
 
 
 class State(TypedDict):
     default: tuple[TensorBackend, Optimizer]
     current: tuple[TensorBackend, Optimizer]
 
 
-class Module(ModuleType):
-    state: State = {
-        'default': (_default_backend, _default_optimizer),
-        'current': (_default_backend, _default_optimizer),
-    }
+class HasState(Protocol):
+    state: State
 
 
-this = Module(__name__)
+this: HasState = sys.modules[__name__]
+this.state = {
+    'default': (None, None),  # type: ignore[typeddict-item]
+    'current': (None, None),  # type: ignore[typeddict-item]
+}
 
 
 def get_backend(default: bool = False) -> tuple[TensorBackend, Optimizer]:
@@ -52,6 +49,13 @@ def get_backend(default: bool = False) -> tuple[TensorBackend, Optimizer]:
     return this.state['current']
 
 
+_default_backend: TensorBackend = BackendRetriever.numpy_backend()
+_default_optimizer: Optimizer = OptimizerRetriever.scipy_optimizer()  # type: ignore[no-untyped-call]
+
+this.state['default'] = (_default_backend, _default_optimizer)
+this.state['current'] = this.state['default']
+
+
 @events.register('change_backend')
 def set_backend(
     backend: str | bytes | TensorBackend,
@@ -193,6 +197,3 @@ def set_backend(
         events.trigger("optimizer_changed")()
     # set up any other globals for backend
     new_backend._setup()
-
-
-sys.modules[__name__] = this

src/pyhf/typing.py

@@ -27,6 +27,7 @@
     "Workspace",
     "Literal",
     "TypedDict",
+    "Protocol",
 )