Type annotations missing for initial_state and final_states; leading to linting errors with Pylint/Pyright

[pascal456]

In

python-statemachine/statemachine/factory.py

Lines 43 to 55 in 50cc5ef

	def _set_special_states(cls):
	if not cls.states:
	return
	initials = [s for s in cls.states if s.initial]
	if len(initials) != 1:
	raise InvalidDefinition(
	_(
	"There should be one and only one initial state. "
	"Your currently have these: {!r}"
	).format([s.id for s in initials])
	)
	cls.initial_state = initials[0]
	cls.final_states = [state for state in cls.states if state.final]

The part

cls.initial_state = initials[0] 
cls.final_states = [state for state in cls.states if state.final] 

is adding the respecting attributes.

We are using those attributes in one of our projects to make checks against the current_state. We find that very handy.

Now we are also using pyright / pylint for linting which gives warnings for the respecting attributes:

Cannot access member "initial_state" for type "StateMachine"
  Member "initial_state" is unknownPylance[reportGeneralTypeIssues](https://github.com/microsoft/pyright/blob/main/docs/configuration.md#reportGeneralTypeIssues)

Seems that the problem here is, that they are added at runtime, which is not handled by static type checkers.

simply adding them as empty arguments in the constructor of the meta class could help with that. Alternatively add them in the class body with type annotations.

So in:

python-statemachine/statemachine/factory.py

Lines 19 to 35 in 50cc5ef

	class StateMachineMetaclass(type):
	def __init__(cls, name: str, bases: Tuple[type], attrs: Dict[str, Any]):
	super().__init__(name, bases, attrs)
	registry.register(cls)
	cls.name = cls.__name__
	cls.states: States = States()
	cls.states_map: Dict[Any, State] = {}
	"""Map of ``state.value`` to the corresponding :ref:`state`."""
	cls._abstract = True
	cls._events: Dict[str, Event] = {}
	cls.add_inherited(bases)
	cls.add_from_attributes(attrs)
	cls._set_special_states()
	cls._check()

those fields are also listed in StateMachine:

python-statemachine/statemachine/statemachine.py

Lines 129 to 130 in 50cc5ef

	"initial_state",
	"final_states",

and are therefore meant to be immutable(?) and could therefore be added to the base class as well.

Suggestion for changes

make changes like this:

class StateMachineMetaclass(type):

    initial_state: State
    final_states: list[State]

    def __init__(cls, name: str, bases: Tuple[type], attrs: Dict[str, Any]):
        super().__init__(name, bases, attrs)
        registry.register(cls)
        cls.name = cls.__name__
        cls.states: States = States()
        cls.states_map: Dict[Any, State] = {}
        """Map of ``state.value`` to the corresponding :ref:`state`."""

        cls._abstract = True
        cls._events: Dict[str, Event] = {}

        cls.add_inherited(bases)
        cls.add_from_attributes(attrs)

        cls._set_special_states()
        cls._check()

[fgmacedo]

Hi @pascal456 , how are you? Thanks for reporting this.

Can you please validate against the branch macedo/improve-metaclass-typehint at #399?

[pascal456]

hi @fgmacedo , fine thanks, hope you too!
wow that was fast! Tested it just now, and works snuggly 🤩
Thank you very much!

[fgmacedo]

Hi there! I'm really glad to hear that you've found it helpful and that it's working well for you. If you have any more questions or need further assistance, feel free to ask. Thanks for your kind words! 😊