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214 lines
6.9 KiB
214 lines
6.9 KiB
from copy import deepcopy
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from typing import Any
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from .callbacks import Callbacks
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from .exceptions import StateMachineError
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from .i18n import _
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from .transition import Transition
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from .transition_list import TransitionList
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class State:
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"""
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A State in a :ref:`StateMachine` describes a particular behavior of the machine.
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When we say that a machine is “in” a state, it means that the machine behaves
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in the way that state describes.
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Args:
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name: A human-readable representation of the state. Default is derived
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from the name of the variable assigned to the state machine class.
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The name is derived from the id using this logic::
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name = id.replace("_", " ").capitalize()
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value: A specific value to the storage and retrieval of states.
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If specified, you can use It to map a more friendly representation to a low-level
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value.
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initial: Set ``True`` if the ``State`` is the initial one. There must be one and only
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one initial state in a statemachine. Defaults to ``False``.
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final: Set ``True`` if represents a final state. A machine can have
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optionally many final states. Final states have no :ref:`transition` starting from It.
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Defaults to ``False``.
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enter: One or more callbacks assigned to be executed when the state is entered.
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See :ref:`actions`.
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exit: One or more callbacks assigned to be executed when the state is exited.
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See :ref:`actions`.
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State is a core component on how this library implements an expressive API to declare
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StateMachines.
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>>> from statemachine import State
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Given a few states...
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>>> draft = State("Draft", initial=True)
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>>> producing = State("Producing")
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>>> closed = State('Closed', final=True)
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Transitions are declared using the :func:`State.to` or :func:`State.from_` (reversed) methods.
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>>> draft.to(producing)
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TransitionList([Transition(State('Draft', ...
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The result is a :ref:`TransitionList`.
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Don't worry about this internal class.
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But the good thing is that it implements the ``OR`` operator to combine transitions,
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so you can use the ``|`` syntax to compound a list of transitions and assign
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to the same event.
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You can declare all transitions for a state in one single line ...
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>>> transitions = draft.to(draft) | producing.to(closed)
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... and you can append additional transitions for a state to previous definitions.
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>>> transitions |= closed.to(draft)
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>>> [(t.source.name, t.target.name) for t in transitions]
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[('Draft', 'Draft'), ('Producing', 'Closed'), ('Closed', 'Draft')]
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There are handy shortcuts that you can use to express this same set of transitions.
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The first one, ``draft.to(draft)``, is also called a :ref:`self-transition`, and can be
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expressed using an alternative syntax:
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>>> draft.to.itself()
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TransitionList([Transition(State('Draft', ...
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You can even pass a list of target states to declare at once all transitions starting
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from the same state.
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>>> transitions = draft.to(draft, producing, closed)
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>>> [(t.source.name, t.target.name) for t in transitions]
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[('Draft', 'Draft'), ('Draft', 'Producing'), ('Draft', 'Closed')]
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"""
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def __init__(
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self,
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name: str = "",
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value: Any = None,
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initial: bool = False,
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final: bool = False,
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enter: Any = None,
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exit: Any = None,
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):
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self.name = name
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self.value = value
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self._initial = initial
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self._final = final
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self._id: str = ""
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self._storage: str = ""
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self.transitions = TransitionList()
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self.enter = Callbacks().add(enter)
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self.exit = Callbacks().add(exit)
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def __eq__(self, other):
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return (
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isinstance(other, State) and self.name == other.name and self.id == other.id
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)
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def __hash__(self):
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return hash(repr(self))
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def _setup(self, machine, resolver):
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self.machine = machine
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self.enter.setup(resolver)
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self.exit.setup(resolver)
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machine.__dict__[self._storage] = self
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return self
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def _add_observer(self, *resolvers):
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for r in resolvers:
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self.enter.add(
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"on_enter_state", resolver=r, prepend=True, suppress_errors=True
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)
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self.enter.add(f"on_enter_{self.id}", resolver=r, suppress_errors=True)
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self.exit.add(
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"on_exit_state", resolver=r, prepend=True, suppress_errors=True
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)
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self.exit.add(f"on_exit_{self.id}", resolver=r, suppress_errors=True)
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def __repr__(self):
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return (
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f"{type(self).__name__}({self.name!r}, id={self.id!r}, value={self.value!r}, "
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f"initial={self.initial!r}, final={self.final!r})"
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)
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def __get__(self, machine, owner):
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if machine and self._storage in machine.__dict__:
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return machine.__dict__[self._storage]
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return self
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def __set__(self, instance, value):
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raise StateMachineError(
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_("State overriding is not allowed. Trying to add '{}' to {}").format(
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value, self.id
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)
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)
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def clone(self):
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return deepcopy(self)
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@property
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def id(self) -> str:
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return self._id
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def _set_id(self, id: str):
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self._id = id
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self._storage = f"_{id}"
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if self.value is None:
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self.value = id
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if not self.name:
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self.name = self._id.replace("_", " ").capitalize()
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def _to_(self, *states: "State", **kwargs):
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transitions = TransitionList(
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Transition(self, state, **kwargs) for state in states
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)
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self.transitions.add_transitions(transitions)
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return transitions
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def _from_(self, *states: "State", **kwargs):
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transitions = TransitionList()
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for origin in states:
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transition = Transition(origin, self, **kwargs)
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origin.transitions.add_transitions(transition)
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transitions.add_transitions(transition)
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return transitions
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def _get_proxy_method_to_itself(self, method):
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def proxy(*states: "State", **kwargs):
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return method(*states, **kwargs)
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def proxy_to_itself(**kwargs):
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return proxy(self, **kwargs)
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proxy.itself = proxy_to_itself
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return proxy
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@property
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def to(self):
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"""Create transitions to the given target states."""
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return self._get_proxy_method_to_itself(self._to_)
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@property
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def from_(self):
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"""Create transitions from the given target states (reversed)."""
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return self._get_proxy_method_to_itself(self._from_)
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@property
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def initial(self):
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return self._initial
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@property
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def final(self):
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return self._final
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@property
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def is_active(self):
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return self.machine.current_state == self
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