from copy import deepcopy
from typing import TYPE_CHECKING
from .callbacks import CallbackGroup
from .callbacks import CallbackPriority
from .callbacks import CallbackSpecList
from .events import Events
from .exceptions import InvalidDefinition
if TYPE_CHECKING:
from .statemachine import State
[docs]
class Transition:
"""A transition holds reference to the source and target state.
Args:
source (State): The origin state of the transition.
target (State): The target state of the transition.
event (Optional[Union[str, List[str]]]): List of designators of events that trigger this
transition. Can be either a list of strings, or a space-separated string list of event
descriptors.
internal (bool): Is the transition internal or external? Internal transitions
don't execute the state entry/exit actions. Default ``False``.
validators (Optional[Union[str, Callable, List[Callable]]]): The validation callbacks to
be invoked before the transition is executed.
cond (Optional[Union[str, Callable, List[Callable]]]): The condition callbacks to be
invoked before the transition is executed that should evaluate to `True`.
unless (Optional[Union[str, Callable, List[Callable]]]): The condition callbacks to be
invoked if the `cond` is False before the transition is executed.
on (Optional[Union[str, Callable, List[Callable]]]): The callbacks to be invoked
when the transition is executed.
before (Optional[Union[str, Callable, List[Callable]]]): The callbacks to be invoked
before the transition is executed.
after (Optional[Union[str, Callable, List[Callable]]]): The callbacks to be invoked
after the transition is executed.
"""
def __init__(
self,
source: "State",
target: "State",
event=None,
internal=False,
validators=None,
cond=None,
unless=None,
on=None,
before=None,
after=None,
):
self.source = source
self.target = target
self.internal = internal
if internal and source is not target:
raise InvalidDefinition("Internal transitions should be self-transitions.")
self._events = Events().add(event)
self._specs = CallbackSpecList()
self.validators = self._specs.grouper(CallbackGroup.VALIDATOR).add(
validators, priority=CallbackPriority.INLINE
)
self.before = self._specs.grouper(CallbackGroup.BEFORE).add(
before, priority=CallbackPriority.INLINE
)
self.on = self._specs.grouper(CallbackGroup.ON).add(on, priority=CallbackPriority.INLINE)
self.after = self._specs.grouper(CallbackGroup.AFTER).add(
after, priority=CallbackPriority.INLINE
)
self.cond = (
self._specs.grouper(CallbackGroup.COND)
.add(cond, priority=CallbackPriority.INLINE, expected_value=True)
.add(unless, priority=CallbackPriority.INLINE, expected_value=False)
)
def __repr__(self):
return (
f"{type(self).__name__}({self.source!r}, {self.target!r}, event={self.event!r}, "
f"internal={self.internal!r})"
)
def __str__(self):
return f"transition {self.event!s} from {self.source!s} to {self.target!s}"
def _setup(self):
before = self.before.add
on = self.on.add
after = self.after.add
before("before_transition", priority=CallbackPriority.GENERIC, is_convention=True)
on("on_transition", priority=CallbackPriority.GENERIC, is_convention=True)
for event in self._events:
same_event_cond = event.is_same_event
before(
f"before_{event}",
priority=CallbackPriority.NAMING,
is_convention=True,
cond=same_event_cond,
)
on(
f"on_{event}",
priority=CallbackPriority.NAMING,
is_convention=True,
cond=same_event_cond,
)
after(
f"after_{event}",
priority=CallbackPriority.NAMING,
is_convention=True,
cond=same_event_cond,
)
after(
"after_transition",
priority=CallbackPriority.AFTER,
is_convention=True,
)
def match(self, event: str):
return self._events.match(event)
@property
def event(self):
return str(self._events)
@property
def events(self):
return self._events
def add_event(self, value):
self._events.add(value)
def _copy_with_args(self, **kwargs):
source = kwargs.pop("source", self.source)
target = kwargs.pop("target", self.target)
event = kwargs.pop("event", self.event)
internal = kwargs.pop("internal", self.internal)
new_transition = Transition(
source=source, target=target, event=event, internal=internal, **kwargs
)
for spec in self._specs:
new_spec = deepcopy(spec)
new_transition._specs.add(new_spec, new_spec.group)
return new_transition