# Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
import collections
from debtcollector import removals
import prettytable
import six
from automaton import _utils as utils
from automaton import exceptions as excp
class State(object):
"""Container that defines needed components of a single state.
Usage of this and the :meth:`~.FiniteMachine.build` 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):
self.name = 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(six.iterkeys(data))
else:
return list(six.iterkeys(data))
class _Jump(object):
"""A FSM transition tracks this data while jumping."""
def __init__(self, name, on_enter, on_exit):
self.name = name
self.on_enter = on_enter
self.on_exit = on_exit
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:`~automaton.runners.Runner.run` method is used). This allows
for two unique ways (these ways can also be intermixed) to use this state
machine when using :py:meth:`~automaton.runners.Runner.run`; 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:`~automaton.runners.Runner.run`
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"])
@removals.removed_kwarg('default_start_state',
message="The usage of 'default_start_state' via"
" the machine constructor is deprecated and will"
" be removed in a future version; usage of"
" the 'default_start_state' property setter is"
" recommended.")
def __init__(self, default_start_state=None):
self._transitions = {}
self._states = collections.OrderedDict()
self._default_start_state = default_start_state
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
@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(state.name,
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 = next_state.name
m.add_transition(state.name, 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 self._current.name
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[self._current.name]['terminal']
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 six.callable(on_enter):
raise ValueError("On enter callback must be callable")
if on_exit is not None:
if not six.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()
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[current.name]:
return False
return True
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 six.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))
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 _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 _post_process_event(self, event, result):
return result
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[current.name][event]
if current.on_exit is not None:
current.on_exit(current.name, event)
if replacement.on_enter is not None:
replacement.on_enter(replacement.name, event)
self._current = replacement
result = self._effect_builder(self._states[replacement.name], event)
return self._post_process_event(event, result)
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'])
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
def __contains__(self, state):
"""Returns if this state exists in the machines known states."""
return state in self._states
def freeze(self):
"""Freezes & stops addition of states, transitions, reactions..."""
self.frozen = True
@property
def states(self):
"""Returns the state names."""
return list(six.iterkeys(self._states))
@property
def events(self):
"""Returns how many events exist."""
c = 0
for state in six.iterkeys(self._states):
c += len(self._transitions[state])
return c
def __iter__(self):
"""Iterates over (start, event, end) transition tuples."""
for state in six.iterkeys(self._states):
for event, target in self._transitions[state].items():
yield (state, event, target.name)
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, target.name]
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()
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, default_start_state=None):
super(HierarchicalFiniteMachine, self).__init__(
default_start_state=default_start_state)
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'))
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
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
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 six.itervalues(self._states):
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