def _pre_process_event(self, event):
current = self._current
if current is None:
raise excp.NotInitialized("Can not process event '%s'; the state"
" machine hasn't been initialized" %
event)
if self._states[current.name]['terminal']:
raise excp.InvalidState("Can not transition from terminal"
" state '%s' on event '%s'" %
(current.name, event))
if event not in self._transitions[current.name]:
raise excp.NotFound("Can not transition from state '%s' on"
" event '%s' (no defined transition)" %
(current.name, event))
def add_transition(self, start, end, event, replace=False):
"""Adds an allowed transition from start -> end for the given event.
:param start: starting state
:param end: ending state
:param event: event that causes start state to
transition to end state
:param replace: replace existing event instead of raising a
:py:class:`~automaton.exceptions.Duplicate` exception
when the transition already exists.
"""
if self.frozen:
raise excp.FrozenMachine()
if start not in self._states:
raise excp.NotFound("Can not add a transition on event '%s' that"
" starts in a undefined state '%s'" %
(event, start))
if end not in self._states:
raise excp.NotFound("Can not add a transition on event '%s' that"
" ends in a undefined state '%s'" %
(event, end))
if self._states[start]['terminal']:
raise excp.InvalidState("Can not add a transition on event '%s'"
" that starts in the terminal state '%s'" %
(event, start))
if event in self._transitions[start] and not replace:
target = self._transitions[start][event]
if target.name != end:
raise excp.Duplicate(
"Cannot add transition from"
" '%(start_state)s' to '%(end_state)s'"
" on event '%(event)s' because a"
" transition from '%(start_state)s'"
" to '%(existing_end_state)s' on"
" event '%(event)s' already exists." % {
'existing_end_state': target.name,
'end_state': end,
'event': event,
'start_state': start
})
else:
target = _Jump(end, self._states[end]['on_enter'],
self._states[start]['on_exit'])
self._transitions[start][event] = target
def initialize(self, start_state=None):
"""Sets up the state machine (sets current state to start state...).
:param start_state: explicit start state to use to initialize the
state machine to. If ``None`` is provided then
the machine's default start state will be used
instead.
"""
if start_state is None:
start_state = self._default_start_state
if start_state not in self._states:
raise excp.NotFound("Can not start from a undefined"
" state '%s'" % (start_state))
if self._states[start_state]['terminal']:
raise excp.InvalidState("Can not start from a terminal"
" state '%s'" % (start_state))
# No on enter will be called, since we are priming the state machine
# and have not really transitioned from anything to get here, we will
# though allow on_exit to be called on the event that causes this
# to be moved from...
self._current = _Jump(start_state, None,
self._states[start_state]['on_exit'])