Source code for automaton.machines

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import collections

import prettytable

from automaton import _utils as utils
from automaton import exceptions as excp

[docs]class State(object): """Container that defines needed components of a single state. Usage of this and the :meth:`` make creating finite state machines that much easier. :ivar name: The name of the state. :ivar is_terminal: Whether this state is terminal (or not). :ivar next_states: Dictionary of 'event' -> 'next state name' (or none). :ivar on_enter: callback that will be called when the state is entered. :ivar on_exit: callback that will be called when the state is exited. """ def __init__(self, name, is_terminal=False, next_states=None, on_enter=None, on_exit=None): = name self.is_terminal = bool(is_terminal) self.next_states = next_states self.on_enter = on_enter self.on_exit = on_exit
def _convert_to_states(state_space): # NOTE(harlowja): if provided dicts, convert them... for state in state_space: if isinstance(state, dict): state = State(**state) yield state def _orderedkeys(data, sort=True): if sort: return sorted(data) else: return list(data) class _Jump(object): """A FSM transition tracks this data while jumping.""" def __init__(self, name, on_enter, on_exit): = name self.on_enter = on_enter self.on_exit = on_exit
[docs]class FiniteMachine(object): """A finite state machine. This state machine can be used to automatically run a given set of transitions and states in response to events (either from callbacks or from generator/iterator send() values, see PEP 342). On each triggered event, a ``on_enter`` and ``on_exit`` callback can also be provided which will be called to perform some type of action on leaving a prior state and before entering a new state. NOTE(harlowja): reactions will *only* be called when the generator/iterator from :py:meth:`~automaton.runners.Runner.run_iter` does *not* send back a new event (they will always be called if the :py:meth:`` method is used). This allows for two unique ways (these ways can also be intermixed) to use this state machine when using :py:meth:``; one where *external* event trigger the next state transition and one where *internal* reaction callbacks trigger the next state transition. The other way to use this state machine is to skip using :py:meth:`` or :py:meth:`~automaton.runners.Runner.run_iter` completely and use the :meth:`~.FiniteMachine.process_event` method explicitly and trigger the events via some *external* functionality/triggers... """ #: The result of processing an event (cause and effect...) Effect = collections.namedtuple('Effect', 'reaction,terminal') @classmethod def _effect_builder(cls, new_state, event): return cls.Effect(new_state['reactions'].get(event), new_state["terminal"]) def __init__(self): self._transitions = {} self._states = collections.OrderedDict() self._default_start_state = None self._current = None self.frozen = False @property def default_start_state(self): """Sets the *default* start state that the machine should use. NOTE(harlowja): this will be used by ``initialize`` but only if that function is not given its own ``start_state`` that overrides this default. """ return self._default_start_state @default_start_state.setter def default_start_state(self, state): if self.frozen: raise excp.FrozenMachine() if state not in self._states: raise excp.NotFound("Can not set the default start state to" " undefined state '%s'" % (state)) self._default_start_state = state
[docs] @classmethod def build(cls, state_space): """Builds a machine from a state space listing. Each element of this list must be an instance of :py:class:`.State` or a ``dict`` with equivalent keys that can be used to construct a :py:class:`.State` instance. """ state_space = list(_convert_to_states(state_space)) m = cls() for state in state_space: m.add_state(, terminal=state.is_terminal, on_enter=state.on_enter, on_exit=state.on_exit) for state in state_space: if state.next_states: for event, next_state in state.next_states.items(): if isinstance(next_state, State): next_state = m.add_transition(, next_state, event) return m
@property def current_state(self): """The current state the machine is in (or none if not initialized).""" if self._current is not None: return return None @property def terminated(self): """Returns whether the state machine is in a terminal state.""" if self._current is None: return False return self._states[]['terminal']
[docs] def add_state(self, state, terminal=False, on_enter=None, on_exit=None): """Adds a given state to the state machine. The ``on_enter`` and ``on_exit`` callbacks, if provided will be expected to take two positional parameters, these being the state being exited (for ``on_exit``) or the state being entered (for ``on_enter``) and a second parameter which is the event that is being processed that caused the state transition. """ if self.frozen: raise excp.FrozenMachine() if state in self._states: raise excp.Duplicate("State '%s' already defined" % state) if on_enter is not None: if not callable(on_enter): raise ValueError("On enter callback must be callable") if on_exit is not None: if not callable(on_exit): raise ValueError("On exit callback must be callable") self._states[state] = { 'terminal': bool(terminal), 'reactions': {}, 'on_enter': on_enter, 'on_exit': on_exit, } self._transitions[state] = collections.OrderedDict()
[docs] def is_actionable_event(self, event): """Check whether the event is actionable in the current state.""" current = self._current if current is None: return False if event not in self._transitions[]: return False return True
[docs] def add_reaction(self, state, event, reaction, *args, **kwargs): """Adds a reaction that may get triggered by the given event & state. Reaction callbacks may (depending on how the state machine is ran) be used after an event is processed (and a transition occurs) to cause the machine to react to the newly arrived at stable state. These callbacks are expected to accept three default positional parameters (although more can be passed in via *args and **kwargs, these will automatically get provided to the callback when it is activated *ontop* of the three default). The three default parameters are the last stable state, the new stable state and the event that caused the transition to this new stable state to be arrived at. The expected result of a callback is expected to be a new event that the callback wants the state machine to react to. This new event may (depending on how the state machine is ran) get processed (and this process typically repeats) until the state machine reaches a terminal state. """ if self.frozen: raise excp.FrozenMachine() if state not in self._states: raise excp.NotFound("Can not add a reaction to event '%s' for an" " undefined state '%s'" % (event, state)) if not callable(reaction): raise ValueError("Reaction callback must be callable") if event not in self._states[state]['reactions']: self._states[state]['reactions'][event] = (reaction, args, kwargs) else: raise excp.Duplicate("State '%s' reaction to event '%s'" " already defined" % (state, event))
[docs] 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 != 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':, '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 _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[]['terminal']: raise excp.InvalidState("Can not transition from terminal" " state '%s' on event '%s'" % (, event)) if event not in self._transitions[]: raise excp.NotFound("Can not transition from state '%s' on" " event '%s' (no defined transition)" % (, event)) def _post_process_event(self, event, result): return result
[docs] def process_event(self, event): """Trigger a state change in response to the provided event. :returns: Effect this is either a :py:class:`.FiniteMachine.Effect` or an ``Effect`` from a subclass of :py:class:`.FiniteMachine`. See the appropriate named tuple for a description of the actual items in the tuple. For example, :py:class:`.FiniteMachine.Effect`'s first item is ``reaction``: one could invoke this reaction's callback to react to the new stable state. :rtype: namedtuple """ self._pre_process_event(event) current = self._current replacement = self._transitions[][event] if current.on_exit is not None: current.on_exit(, event) if replacement.on_enter is not None: replacement.on_enter(, event) self._current = replacement result = self._effect_builder(self._states[], event) return self._post_process_event(event, result)
[docs] 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'])
[docs] def copy(self, shallow=False, unfreeze=False): """Copies the current state machine. NOTE(harlowja): the copy will be left in an *uninitialized* state. NOTE(harlowja): when a shallow copy is requested the copy will share the same transition table and state table as the source; this can be advantageous if you have a machine and transitions + states that is defined somewhere and want to use copies to run with (the copies have the current state that is different between machines). """ c = type(self)() c._default_start_state = self._default_start_state if unfreeze and self.frozen: c.frozen = False else: c.frozen = self.frozen if not shallow: for state, data in self._states.items(): copied_data = data.copy() copied_data['reactions'] = copied_data['reactions'].copy() c._states[state] = copied_data for state, data in self._transitions.items(): c._transitions[state] = data.copy() else: c._transitions = self._transitions c._states = self._states return c
[docs] def __contains__(self, state): """Returns if this state exists in the machines known states.""" return state in self._states
[docs] def freeze(self): """Freezes & stops addition of states, transitions, reactions...""" self.frozen = True
@property def states(self): """Returns the state names.""" return list(self._states) @property def events(self): """Returns how many events exist.""" c = 0 for state in self._states: c += len(self._transitions[state]) return c
[docs] def __iter__(self): """Iterates over (start, event, end) transition tuples.""" for state in self._states: for event, target in self._transitions[state].items(): yield (state, event,
[docs] def pformat(self, sort=True, empty='.'): """Pretty formats the state + transition table into a string. NOTE(harlowja): the sort parameter can be provided to sort the states and transitions by sort order; with it being provided as false the rows will be iterated in addition order instead. """ tbl = prettytable.PrettyTable(["Start", "Event", "End", "On Enter", "On Exit"]) for state in _orderedkeys(self._states, sort=sort): prefix_markings = [] if self.current_state == state: prefix_markings.append("@") postfix_markings = [] if self.default_start_state == state: postfix_markings.append("^") if self._states[state]['terminal']: postfix_markings.append("$") pretty_state = "%s%s" % ("".join(prefix_markings), state) if postfix_markings: pretty_state += "[%s]" % "".join(postfix_markings) if self._transitions[state]: for event in _orderedkeys(self._transitions[state], sort=sort): target = self._transitions[state][event] row = [pretty_state, event,] if target.on_enter is not None: row.append(utils.get_callback_name(target.on_enter)) else: row.append(empty) if target.on_exit is not None: row.append(utils.get_callback_name(target.on_exit)) else: row.append(empty) tbl.add_row(row) else: on_enter = self._states[state]['on_enter'] if on_enter is not None: on_enter = utils.get_callback_name(on_enter) else: on_enter = empty on_exit = self._states[state]['on_exit'] if on_exit is not None: on_exit = utils.get_callback_name(on_exit) else: on_exit = empty tbl.add_row([pretty_state, empty, empty, on_enter, on_exit]) return tbl.get_string()
[docs]class HierarchicalFiniteMachine(FiniteMachine): """A fsm that understands how to run in a hierarchical mode.""" #: The result of processing an event (cause and effect...) Effect = collections.namedtuple('Effect', 'reaction,terminal,machine') def __init__(self): super(HierarchicalFiniteMachine, self).__init__() self._nested_machines = {} @classmethod def _effect_builder(cls, new_state, event): return cls.Effect(new_state['reactions'].get(event), new_state["terminal"], new_state.get('machine'))
[docs] def add_state(self, state, terminal=False, on_enter=None, on_exit=None, machine=None): """Adds a given state to the state machine. :param machine: the nested state machine that will be transitioned into when this state is entered :type machine: :py:class:`.FiniteMachine` Further arguments are interpreted as for :py:meth:`.FiniteMachine.add_state`. """ if machine is not None and not isinstance(machine, FiniteMachine): raise ValueError( "Nested state machines must themselves be state machines") super(HierarchicalFiniteMachine, self).add_state( state, terminal=terminal, on_enter=on_enter, on_exit=on_exit) if machine is not None: self._states[state]['machine'] = machine self._nested_machines[state] = machine
[docs] def copy(self, shallow=False, unfreeze=False): c = super(HierarchicalFiniteMachine, self).copy(shallow=shallow, unfreeze=unfreeze) if shallow: c._nested_machines = self._nested_machines else: c._nested_machines = self._nested_machines.copy() return c
[docs] def initialize(self, start_state=None, nested_start_state_fetcher=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. :param nested_start_state_fetcher: A callback that can return start states for any nested machines **only**. If not ``None`` then it will be provided a single argument, the machine to provide a starting state for and it is expected to return a starting state (or ``None``) for each machine called with. Do note that this callback will also be passed to other nested state machines as well, so it will also be used to initialize any state machines they contain (recursively). """ super(HierarchicalFiniteMachine, self).initialize( start_state=start_state) for data in self._states.values(): if 'machine' in data: nested_machine = data['machine'] nested_start_state = None if nested_start_state_fetcher is not None: nested_start_state = nested_start_state_fetcher( nested_machine) if isinstance(nested_machine, HierarchicalFiniteMachine): nested_machine.initialize( start_state=nested_start_state, nested_start_state_fetcher=nested_start_state_fetcher) else: nested_machine.initialize(start_state=nested_start_state)
@property def nested_machines(self): """Dictionary of **all** nested state machines this machine may use.""" return self._nested_machines