Furthur simplipy _create_state_instant only create state from class

src/plumpy/base/state_machine.py

@@ -20,7 +20,6 @@
     Set,
     Type,
     Union,
-    cast,
 )
 
 from plumpy.futures import Future
@@ -325,8 +324,18 @@ def _fire_state_event(self, hook: Hashable, state: Optional[State]) -> None:
     def on_terminated(self) -> None:
         """Called when a terminal state is entered"""
 
-    def transition_to(self, new_state: Union[Hashable, State, Type[State]], *args: Any, **kwargs: Any) -> None:
-        assert not self._transitioning, 'Cannot call transition_to when already transitioning state'
+    def transition_to(
+        self, new_state: Union[State, Type[State]], *args: Any, **kwargs: Any
+    ) -> None:
+        """Transite to the new state.
+
+        The new target state will be create lazily when the state
+        is not yet instantiated, which will happened for states not in the expect path such as
+        pause and kill.
+        """
+        assert (
+            not self._transitioning
+        ), "Cannot call transition_to when already transitioning state"
 
         initial_state_label = self._state.LABEL if self._state is not None else None
         label = None
@@ -389,6 +398,10 @@ def set_debug(self, enabled: bool) -> None:
         self._debug: bool = enabled
 
     def create_state(self, state_label: Hashable, *args: Any, **kwargs: Any) -> State:
+        # XXX: this method create state from label, which is duplicate as _create_state_instance and less generic
+        # because the label is defined after the state and required to be know before calling this function.
+        # This method should be replaced by `_create_state_instance`.
+        # aiida-core using this method for its Waiting state override.
         try:
             return self.get_states_map()[state_label](self, *args, **kwargs)
         except KeyError:
@@ -422,15 +435,9 @@ def _enter_next_state(self, next_state: State) -> None:
         self._fire_state_event(StateEventHook.ENTERED_STATE, last_state)
 
     def _create_state_instance(
-        self, state: Union[Hashable, Type[State]], *args: Any, **kwargs: Any
+        self, state_cls: type[State], *args: Any, **kwargs: Any
     ) -> State:
-        # build from state class
-        if inspect.isclass(state) and issubclass(state, State):
-            state_cls = state
-        else:
-            try:
-                state_cls = self.get_states_map()[cast(Hashable, state)]  # pylint: disable=unsubscriptable-object
-            except KeyError:
-                raise ValueError(f"{state} is not a valid state")
+        if state_cls.LABEL not in self.get_states_map():
+            raise ValueError(f"{state_cls.LABEL} is not a valid state")
 
         return state_cls(self, *args, **kwargs)

src/plumpy/processes.py

@@ -831,7 +831,7 @@ def on_finish(self, result: Any, successful: bool) -> None:
         if successful:
             validation_error = self.spec().outputs.validate(self.outputs)
             if validation_error:
-                raise StateEntryFailed(process_states.ProcessState.FINISHED, result, False)
+                raise StateEntryFailed(process_states.Finished, result, False)
 
         self.future().set_result(self.outputs)
 
@@ -1016,7 +1016,7 @@ def transition_failed(
         if final_state == process_states.ProcessState.CREATED:
             raise exception.with_traceback(trace)
 
-        self.transition_to(process_states.ProcessState.EXCEPTED, exception, trace)
+        self.transition_to(process_states.Excepted, exception, trace)
 
     def pause(self, msg: Union[str, None] = None) -> Union[bool, futures.CancellableAction]:
         """Pause the process.
@@ -1081,7 +1081,7 @@ def do_kill(_next_state: process_states.State) -> Any:
                 try:
                     # Ignore the next state
                     # __import__('ipdb').set_trace()
-                    self.transition_to(process_states.ProcessState.KILLED, exception)
+                    self.transition_to(process_states.Killed, exception)
                     return True
                 finally:
                     self._killing = None
@@ -1133,7 +1133,7 @@ def fail(self, exception: Optional[BaseException], trace_back: Optional[Tracebac
         :param exception: The exception that caused the failure
         :param trace_back: Optional exception traceback
         """
-        self.transition_to(process_states.ProcessState.EXCEPTED, exception, trace_back)
+        self.transition_to(process_states.Excepted, exception, trace_back)
 
     def kill(self, msg: Optional[MessageType] = None) -> Union[bool, asyncio.Future]:
         """
@@ -1161,7 +1161,7 @@ def kill(self, msg: Optional[MessageType] = None) -> Union[bool, asyncio.Future]
             self._state.interrupt(interrupt_exception)
             return cast(futures.CancellableAction, self._interrupt_action)
 
-        self.transition_to(process_states.ProcessState.KILLED, msg)
+        self.transition_to(process_states.Killed, msg)
         return True
 
     @property