544 lines
24 KiB
Python
544 lines
24 KiB
Python
# Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import collections
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from debtcollector import removals
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import prettytable
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import six
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from automaton import _utils as utils
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from automaton import exceptions as excp
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class State(object):
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"""Container that defines needed components of a single state.
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Usage of this and the :meth:`~.FiniteMachine.build` make creating finite
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state machines that much easier.
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:ivar name: The name of the state.
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:ivar is_terminal: Whether this state is terminal (or not).
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:ivar next_states: Dictionary of 'event' -> 'next state name' (or none).
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:ivar on_enter: callback that will be called when the state is entered.
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:ivar on_exit: callback that will be called when the state is exited.
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"""
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def __init__(self, name,
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is_terminal=False, next_states=None,
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on_enter=None, on_exit=None):
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self.name = name
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self.is_terminal = bool(is_terminal)
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self.next_states = next_states
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self.on_enter = on_enter
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self.on_exit = on_exit
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def _convert_to_states(state_space):
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# NOTE(harlowja): if provided dicts, convert them...
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for state in state_space:
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if isinstance(state, dict):
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state = State(**state)
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yield state
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def _orderedkeys(data, sort=True):
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if sort:
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return sorted(six.iterkeys(data))
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else:
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return list(six.iterkeys(data))
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class _Jump(object):
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"""A FSM transition tracks this data while jumping."""
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def __init__(self, name, on_enter, on_exit):
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self.name = name
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self.on_enter = on_enter
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self.on_exit = on_exit
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class FiniteMachine(object):
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"""A finite state machine.
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This state machine can be used to automatically run a given set of
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transitions and states in response to events (either from callbacks or from
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generator/iterator send() values, see PEP 342). On each triggered event, a
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``on_enter`` and ``on_exit`` callback can also be provided which will be
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called to perform some type of action on leaving a prior state and before
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entering a new state.
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NOTE(harlowja): reactions will *only* be called when the generator/iterator
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from :py:meth:`~automaton.runners.Runner.run_iter` does *not* send
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back a new event (they will always be called if the
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:py:meth:`~automaton.runners.Runner.run` method is used). This allows
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for two unique ways (these ways can also be intermixed) to use this state
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machine when using :py:meth:`~automaton.runners.Runner.run`; one
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where *external* event trigger the next state transition and one
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where *internal* reaction callbacks trigger the next state
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transition. The other way to use this
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state machine is to skip using :py:meth:`~automaton.runners.Runner.run`
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or :py:meth:`~automaton.runners.Runner.run_iter`
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completely and use the :meth:`~.FiniteMachine.process_event` method
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explicitly and trigger the events via
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some *external* functionality/triggers...
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"""
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#: The result of processing an event (cause and effect...)
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Effect = collections.namedtuple('Effect', 'reaction,terminal')
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@classmethod
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def _effect_builder(cls, new_state, event):
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return cls.Effect(new_state['reactions'].get(event),
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new_state["terminal"])
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@removals.removed_kwarg('default_start_state',
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message="The usage of 'default_start_state' via"
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" the machine constructor is deprecated and will"
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" be removed in a future version; usage of"
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" the 'default_start_state' property setter is"
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" recommended.")
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def __init__(self, default_start_state=None):
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self._transitions = {}
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self._states = collections.OrderedDict()
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self._default_start_state = default_start_state
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self._current = None
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self.frozen = False
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@property
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def default_start_state(self):
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"""Sets the *default* start state that the machine should use.
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NOTE(harlowja): this will be used by ``initialize`` but only if that
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function is not given its own ``start_state`` that overrides this
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default.
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"""
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return self._default_start_state
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@default_start_state.setter
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def default_start_state(self, state):
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if self.frozen:
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raise excp.FrozenMachine()
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if state not in self._states:
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raise excp.NotFound("Can not set the default start state to"
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" undefined state '%s'" % (state))
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self._default_start_state = state
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@classmethod
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def build(cls, state_space):
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"""Builds a machine from a state space listing.
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Each element of this list must be an instance
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of :py:class:`.State` or a ``dict`` with equivalent keys that
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can be used to construct a :py:class:`.State` instance.
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"""
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state_space = list(_convert_to_states(state_space))
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m = cls()
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for state in state_space:
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m.add_state(state.name,
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terminal=state.is_terminal,
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on_enter=state.on_enter,
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on_exit=state.on_exit)
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for state in state_space:
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if state.next_states:
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for event, next_state in state.next_states.items():
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if isinstance(next_state, State):
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next_state = next_state.name
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m.add_transition(state.name, next_state, event)
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return m
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@property
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def current_state(self):
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"""The current state the machine is in (or none if not initialized)."""
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if self._current is not None:
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return self._current.name
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return None
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@property
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def terminated(self):
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"""Returns whether the state machine is in a terminal state."""
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if self._current is None:
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return False
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return self._states[self._current.name]['terminal']
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def add_state(self, state, terminal=False, on_enter=None, on_exit=None):
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"""Adds a given state to the state machine.
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The ``on_enter`` and ``on_exit`` callbacks, if provided will be
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expected to take two positional parameters, these being the state
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being exited (for ``on_exit``) or the state being entered (for
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``on_enter``) and a second parameter which is the event that is
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being processed that caused the state transition.
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"""
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if self.frozen:
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raise excp.FrozenMachine()
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if state in self._states:
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raise excp.Duplicate("State '%s' already defined" % state)
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if on_enter is not None:
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if not six.callable(on_enter):
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raise ValueError("On enter callback must be callable")
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if on_exit is not None:
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if not six.callable(on_exit):
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raise ValueError("On exit callback must be callable")
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self._states[state] = {
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'terminal': bool(terminal),
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'reactions': {},
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'on_enter': on_enter,
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'on_exit': on_exit,
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}
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self._transitions[state] = collections.OrderedDict()
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def is_actionable_event(self, event):
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"""Check whether the event is actionable in the current state."""
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current = self._current
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if current is None:
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return False
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if event not in self._transitions[current.name]:
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return False
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return True
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def add_reaction(self, state, event, reaction, *args, **kwargs):
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"""Adds a reaction that may get triggered by the given event & state.
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Reaction callbacks may (depending on how the state machine is ran) be
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used after an event is processed (and a transition occurs) to cause the
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machine to react to the newly arrived at stable state.
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These callbacks are expected to accept three default positional
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parameters (although more can be passed in via *args and **kwargs,
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these will automatically get provided to the callback when it is
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activated *ontop* of the three default). The three default parameters
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are the last stable state, the new stable state and the event that
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caused the transition to this new stable state to be arrived at.
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The expected result of a callback is expected to be a new event that
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the callback wants the state machine to react to. This new event
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may (depending on how the state machine is ran) get processed (and
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this process typically repeats) until the state machine reaches a
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terminal state.
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"""
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if self.frozen:
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raise excp.FrozenMachine()
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if state not in self._states:
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raise excp.NotFound("Can not add a reaction to event '%s' for an"
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" undefined state '%s'" % (event, state))
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if not six.callable(reaction):
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raise ValueError("Reaction callback must be callable")
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if event not in self._states[state]['reactions']:
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self._states[state]['reactions'][event] = (reaction, args, kwargs)
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else:
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raise excp.Duplicate("State '%s' reaction to event '%s'"
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" already defined" % (state, event))
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def add_transition(self, start, end, event, replace=False):
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"""Adds an allowed transition from start -> end for the given event.
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:param start: starting state
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:param end: ending state
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:param event: event that causes start state to
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transition to end state
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:param replace: replace existing event instead of raising a
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:py:class:`~automaton.exceptions.Duplicate` exception
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when the transition already exists.
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"""
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if self.frozen:
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raise excp.FrozenMachine()
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if start not in self._states:
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raise excp.NotFound("Can not add a transition on event '%s' that"
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" starts in a undefined state '%s'"
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% (event, start))
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if end not in self._states:
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raise excp.NotFound("Can not add a transition on event '%s' that"
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" ends in a undefined state '%s'"
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% (event, end))
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if self._states[start]['terminal']:
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raise excp.InvalidState("Can not add a transition on event '%s'"
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" that starts in the terminal state '%s'"
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% (event, start))
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if event in self._transitions[start] and not replace:
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target = self._transitions[start][event]
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if target.name != end:
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raise excp.Duplicate("Cannot add transition from"
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" '%(start_state)s' to '%(end_state)s'"
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" on event '%(event)s' because a"
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" transition from '%(start_state)s'"
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" to '%(existing_end_state)s' on"
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" event '%(event)s' already exists."
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% {'existing_end_state': target.name,
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'end_state': end, 'event': event,
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'start_state': start})
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else:
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target = _Jump(end, self._states[end]['on_enter'],
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self._states[start]['on_exit'])
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self._transitions[start][event] = target
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def _pre_process_event(self, event):
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current = self._current
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if current is None:
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raise excp.NotInitialized("Can not process event '%s'; the state"
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" machine hasn't been initialized"
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% event)
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if self._states[current.name]['terminal']:
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raise excp.InvalidState("Can not transition from terminal"
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" state '%s' on event '%s'"
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% (current.name, event))
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if event not in self._transitions[current.name]:
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raise excp.NotFound("Can not transition from state '%s' on"
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" event '%s' (no defined transition)"
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% (current.name, event))
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def _post_process_event(self, event, result):
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return result
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def process_event(self, event):
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"""Trigger a state change in response to the provided event.
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:returns: Effect this is either a :py:class:`.FiniteMachine.Effect` or
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an ``Effect`` from a subclass of :py:class:`.FiniteMachine`.
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See the appropriate named tuple for a description of the
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actual items in the tuple. For
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example, :py:class:`.FiniteMachine.Effect`'s
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first item is ``reaction``: one could invoke this reaction's
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callback to react to the new stable state.
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:rtype: namedtuple
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"""
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self._pre_process_event(event)
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current = self._current
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replacement = self._transitions[current.name][event]
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if current.on_exit is not None:
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current.on_exit(current.name, event)
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if replacement.on_enter is not None:
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replacement.on_enter(replacement.name, event)
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self._current = replacement
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result = self._effect_builder(self._states[replacement.name], event)
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return self._post_process_event(event, result)
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def initialize(self, start_state=None):
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"""Sets up the state machine (sets current state to start state...).
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:param start_state: explicit start state to use to initialize the
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state machine to. If ``None`` is provided then
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the machine's default start state will be used
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instead.
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"""
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if start_state is None:
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start_state = self._default_start_state
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if start_state not in self._states:
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raise excp.NotFound("Can not start from a undefined"
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" state '%s'" % (start_state))
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if self._states[start_state]['terminal']:
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raise excp.InvalidState("Can not start from a terminal"
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" state '%s'" % (start_state))
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# No on enter will be called, since we are priming the state machine
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# and have not really transitioned from anything to get here, we will
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# though allow on_exit to be called on the event that causes this
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# to be moved from...
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self._current = _Jump(start_state, None,
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self._states[start_state]['on_exit'])
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def copy(self, shallow=False, unfreeze=False):
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"""Copies the current state machine.
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NOTE(harlowja): the copy will be left in an *uninitialized* state.
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NOTE(harlowja): when a shallow copy is requested the copy will share
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the same transition table and state table as the
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source; this can be advantageous if you have a machine
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and transitions + states that is defined somewhere
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and want to use copies to run with (the copies have
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the current state that is different between machines).
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"""
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c = type(self)()
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c._default_start_state = self._default_start_state
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if unfreeze and self.frozen:
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c.frozen = False
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else:
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c.frozen = self.frozen
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if not shallow:
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for state, data in self._states.items():
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copied_data = data.copy()
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copied_data['reactions'] = copied_data['reactions'].copy()
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c._states[state] = copied_data
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for state, data in self._transitions.items():
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c._transitions[state] = data.copy()
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else:
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c._transitions = self._transitions
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c._states = self._states
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return c
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def __contains__(self, state):
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"""Returns if this state exists in the machines known states."""
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return state in self._states
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def freeze(self):
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"""Freezes & stops addition of states, transitions, reactions..."""
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self.frozen = True
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@property
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def states(self):
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"""Returns the state names."""
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return list(six.iterkeys(self._states))
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@property
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def events(self):
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"""Returns how many events exist."""
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c = 0
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for state in six.iterkeys(self._states):
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c += len(self._transitions[state])
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return c
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def __iter__(self):
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"""Iterates over (start, event, end) transition tuples."""
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for state in six.iterkeys(self._states):
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for event, target in self._transitions[state].items():
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yield (state, event, target.name)
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def pformat(self, sort=True, empty='.'):
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"""Pretty formats the state + transition table into a string.
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NOTE(harlowja): the sort parameter can be provided to sort the states
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and transitions by sort order; with it being provided as false the rows
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will be iterated in addition order instead.
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"""
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tbl = prettytable.PrettyTable(["Start", "Event", "End",
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"On Enter", "On Exit"])
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for state in _orderedkeys(self._states, sort=sort):
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prefix_markings = []
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if self.current_state == state:
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prefix_markings.append("@")
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postfix_markings = []
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if self.default_start_state == state:
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postfix_markings.append("^")
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if self._states[state]['terminal']:
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postfix_markings.append("$")
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pretty_state = "%s%s" % ("".join(prefix_markings), state)
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if postfix_markings:
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pretty_state += "[%s]" % "".join(postfix_markings)
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if self._transitions[state]:
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for event in _orderedkeys(self._transitions[state],
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sort=sort):
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target = self._transitions[state][event]
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row = [pretty_state, event, target.name]
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if target.on_enter is not None:
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row.append(utils.get_callback_name(target.on_enter))
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else:
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row.append(empty)
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if target.on_exit is not None:
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row.append(utils.get_callback_name(target.on_exit))
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else:
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row.append(empty)
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tbl.add_row(row)
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else:
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on_enter = self._states[state]['on_enter']
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if on_enter is not None:
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on_enter = utils.get_callback_name(on_enter)
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else:
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on_enter = empty
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on_exit = self._states[state]['on_exit']
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if on_exit is not None:
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on_exit = utils.get_callback_name(on_exit)
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else:
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on_exit = empty
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tbl.add_row([pretty_state, empty, empty, on_enter, on_exit])
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return tbl.get_string()
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class HierarchicalFiniteMachine(FiniteMachine):
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"""A fsm that understands how to run in a hierarchical mode."""
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#: The result of processing an event (cause and effect...)
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Effect = collections.namedtuple('Effect',
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'reaction,terminal,machine')
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def __init__(self, default_start_state=None):
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super(HierarchicalFiniteMachine, self).__init__(
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default_start_state=default_start_state)
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self._nested_machines = {}
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@classmethod
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def _effect_builder(cls, new_state, event):
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return cls.Effect(new_state['reactions'].get(event),
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new_state["terminal"], new_state.get('machine'))
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def add_state(self, state,
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terminal=False, on_enter=None, on_exit=None, machine=None):
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"""Adds a given state to the state machine.
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:param machine: the nested state machine that will be transitioned
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into when this state is entered
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:type machine: :py:class:`.FiniteMachine`
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Further arguments are interpreted as
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for :py:meth:`.FiniteMachine.add_state`.
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"""
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if machine is not None and not isinstance(machine, FiniteMachine):
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raise ValueError(
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"Nested state machines must themselves be state machines")
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super(HierarchicalFiniteMachine, self).add_state(
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state, terminal=terminal, on_enter=on_enter, on_exit=on_exit)
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if machine is not None:
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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
|