Metadata-Version: 2.1
Name: cs.fsm
Version: 20240519
Summary: Basic Finite State Machine (FSM) tools.
Author-email: Cameron Simpson <cs@cskk.id.au>
License: GNU General Public License v3 or later (GPLv3+)
Project-URL: URL, https://bitbucket.org/cameron_simpson/css/commits/all
Keywords: python3
Platform: UNKNOWN
Classifier: Programming Language :: Python
Classifier: Programming Language :: Python :: 3
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: Operating System :: OS Independent
Classifier: Topic :: Software Development :: Libraries :: Python Modules
Classifier: License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)
Description-Content-Type: text/markdown

Basic Finite State Machine (FSM) tools.

*Latest release 20240519*:
FSM: default for FSM_DEFAULT_STATE is the first key from FSM_TRANSITIONS (relies on ordered dicts, so Python 3.6 onward).

## Class `FSM(cs.gvutils.DOTNodeMixin)`

Base class for a finite state machine (FSM).

The allowed states and transitions are defined by the class
attribute `FSM_TRANSITIONS`, a mapping of
*state*->*event*->*new_state*.

Each instance has the following attributes:
* `fsm_state`: the current state value.
* `fsm_history`: an optional iterable of `FSMTransitionEvent`
  state transitions recorded by the `fsm_event` method.
  Usually this would be `None` (the default) or a `list`.

*Method `FSM.__init__(self, state=None, *, history=None, lock=None, transitions=None)`*:
Initialise the `FSM` from:
* `state`: optional _positional_ parameter for the initial state,
  default `self.FSM_DEFAULT_STATE` or the first key from `self.FSM_TRANSITIONS`
* `history`: an optional object to record state transition
  history, default `None`; if not `None` this should be an
  iterable object with a `.append(entry)` method such as a
  `list`.
* `lock`: an optional mutex to control access;
  if presupplied and shared with the caller
  it should probably be an `RLock`;
  the default is a `Lock`, which is enough for `FSM` private use
* `transitions`: optional *state*->*event*->*state* mapping;
  if provided, this will override the class `FSM_TRANSITIONS` mapping

Note that the `FSM` base class does not provide a
`FSM_DEFAULT_STATE` attribute; a default `state` value of
`None` will leave `.fsm_state` _unset_.

This behaviour is is chosen mostly to support subclasses
with unusual behaviour, particularly Django's `Model` class
whose `refresh_from_db` method seems to not refresh fields
which already exist, and setting `.fsm_state` from a
`FSM_DEFAULT_STATE` class attribute thus breaks this method.
Subclasses of this class and `Model` should _not_ provide a
`FSM_DEFAULT_STATE` attribute, instead relying on the field
definition to provide this default in the usual way.

*Method `FSM.__getattr__(self, attr)`*:
Provide the following attributes:
- present the state names as attributes, for example:
  `self.PENDING=='PENDING'` if there is a `'PENDING'` state
- present `is_`*statename* as a Boolean testing whether
  `self.fsm_state==`*statename*`.upper()`
- a callable calling `self.fsm_event(attr)` if `attr`
  is an event name for the current state
Fall back to the superclass `__getattr__`.

*Property `FSM.dot_node_palette_key`*:
Default palette index is `self.fsm_state`,
overriding `DOTNodeMixin.dot_node_palette_key`.

*Method `FSM.fsm_as_svg(self, layout=None, history_style=None, **dot_kw)`*:
Render the state transition diagram as SVG.

*Method `FSM.fsm_callback(self, state, callback)`*:
Register a callback to be called immediately on transition
to `state` as `callback(self,FSMEventTransition)`.
The special `state` value `FSM.FSM_ANY_STATE` may be supplied
to register a callback which fires for every state transition.

    >>> fsm = FSM('state1',transitions={
    ...   'state1':{'ev_a':'state2'},
    ...   'state2':{'ev_b':'state1'},
    ... })
    >>> fsm.fsm_callback('state2',lambda task, transition: print(task, transition))
    >>> fsm.fsm_callback(FSM.FSM_ANY_STATE,lambda task, transition: print("ANY", task, transition))
    >>> fsm.ev_a(foo=3) # doctest: +ELLIPSIS
    ANY FSM:state2 FSMTransitionEvent(old_state='state1', new_state='state2', event='ev_a', when=..., extra={'foo': 3})
    FSM:state2 FSMTransitionEvent(old_state='state1', new_state='state2', event='ev_a', when=..., extra={'foo': 3})
    'state2'
    >>> fsm.ev_b(foo=4) # doctest: +ELLIPSIS
    ANY FSM:state1 FSMTransitionEvent(old_state='state2', new_state='state1', event='ev_b', when=..., extra={'foo': 4})
    'state1'

*Method `FSM.fsm_callback_discard(self, state, callback)`*:
Deregister a callback for `state`.

*Property `FSM.fsm_dot`*:
A DOT syntax description of `self.FSM_TRANSITIONS`.

*Method `FSM.fsm_event(self, event, **extra)`*:
Transition the FSM from the current state to a new state based on `event`.
Call any callbacks associated with the new state.
Returns the new state.

Optional information may be passed as keyword arguments.

A `transition` instance of `FSMTransitionEvent` is created
with the following attributes:
* `old_state`: the state when `fsm_event` was called
* `new_state`: the new state
* `event`: the `event`
* `when`: a UNIX timestamp from `time.time()`
* `extra`: a `dict` with the `extra` information
If `self.fsm_history` is not `None`,
`transition` is appended to it.
If there are callbacks for `new_state` or `FSM.FSM_ANY_STATE`,
call each callback as `callback(self,transition)`.

*Method `FSM.fsm_event_is_allowed(self, event)`*:
Test whether `event` is permitted in the current state.
This can be handy as a pretest.

*Property `FSM.fsm_events`*:
Return a list of the events valid for the current state.

*Property `FSM.fsm_history`*:
History property wrapping private attribute.
This aids subclassing where the history is not a local attribute.

*Method `FSM.fsm_print(self, file=None, fmt=None, layout=None, **dot_kw)`*:
Print the state transition diagram to `file`, default `sys.stdout`,
in format `fmt` using the engine specified by `layout`, default `'dot'`.
This is a wrapper for `cs.gvutils.gvprint`.

*Property `FSM.fsm_svg`*:
The state transition diagram as SVG.

*Method `FSM.fsm_transitions_as_dot(self, fsm_transitions=None, *, sep='\n', graph_name=None, history_style=None)`*:
Compute a DOT syntax graph description from a transitions dictionary.

        Parameters:
        * `fsm_transitions`: optional mapping of *state*->*event*->*state*,
          default `self.FSM_TRANSITIONS`
        * `sep`: optional separator between "lines", default `'
'`
        * `graph_name`: optional name for the graph, default the class name
        * `history_style`: optional style mapping for event transition history,
          used to style edges which have been traversed

## Class `FSMError(builtins.Exception)`

An exception associated with an `FSM`.

These have a `.fsm` attribute storing an (optional) `FSM`
reference supplied at initialisation.

## `FSMSubType = ~FSMSubType`

Type variable.

Usage::

  T = TypeVar('T')  # Can be anything
  A = TypeVar('A', str, bytes)  # Must be str or bytes

Type variables exist primarily for the benefit of static type
checkers.  They serve as the parameters for generic types as well
as for generic function definitions.  See class Generic for more
information on generic types.  Generic functions work as follows:

  def repeat(x: T, n: int) -> List[T]:
      '''Return a list containing n references to x.'''
      return [x]*n

  def longest(x: A, y: A) -> A:
      '''Return the longest of two strings.'''
      return x if len(x) >= len(y) else y

The latter example's signature is essentially the overloading
of (str, str) -> str and (bytes, bytes) -> bytes.  Also note
that if the arguments are instances of some subclass of str,
the return type is still plain str.

At runtime, isinstance(x, T) and issubclass(C, T) will raise TypeError.

Type variables defined with covariant=True or contravariant=True
can be used to declare covariant or contravariant generic types.
See PEP 484 for more details. By default generic types are invariant
in all type variables.

Type variables can be introspected. e.g.:

  T.__name__ == 'T'
  T.__constraints__ == ()
  T.__covariant__ == False
  T.__contravariant__ = False
  A.__constraints__ == (str, bytes)

Note that only type variables defined in global scope can be pickled.

## Class `FSMTransitionEvent(builtins.tuple)`

FSMTransitionEvent(old_state, new_state, event, when, extra)

*Property `FSMTransitionEvent.event`*:
Alias for field number 2

*Property `FSMTransitionEvent.extra`*:
Alias for field number 4

*Property `FSMTransitionEvent.new_state`*:
Alias for field number 1

*Property `FSMTransitionEvent.old_state`*:
Alias for field number 0

*Property `FSMTransitionEvent.when`*:
Alias for field number 3

# Release Log



*Release 20240519*:
FSM: default for FSM_DEFAULT_STATE is the first key from FSM_TRANSITIONS (relies on ordered dicts, so Python 3.6 onward).

*Release 20240316*:
Fixed release upload artifacts.

*Release 20240305*:
FSM.__getattr__: return None for missing self.fsm_state, happens in too-early call to __str__.

*Release 20231020*:
FSM.__getattr__: known transition names no longerfall through to the superclass if not valid for the current state.

*Release 20231018*:
* FSM.fsm_transitions_as_dot: new optional history_style parameter to style transitioned edges.
* FSM.fsm_as_svg: plumb optional history_style parameter.

*Release 20230816.3*:
Bump cs.gvutils requirement.

*Release 20230816.2*:
FSM.fsm_transitions_as_dot: bugfix: the style needs "style=filled" as well as the fillcolor.

*Release 20230816.1*:
FSM.fsm_transitions_as_dot: now an instance method so that we can colour the current state.

*Release 20230816*:
FSM: new fsm_as_svg method and fsm_svg property.

*Release 20221118*:
* FSM.__init__: make state optional, default from self.FSM_DEFAULT_STATE - now all args are optional.
* FSM.__init__: if the state is None or not supplied, do not set .fsm_state at all; add explaination for this weird design choice.
* FSM.__getattr__: only generate event methods for events with public names (no leading underscore).
* FSM: new .fsm_history property, aiding subclassing elsewhere.
* FSM: drop dot_node_fillcolor, now provided by DOTNodeMixin.__getattr__, provide dot_node_palette_key using self.fsm_state.
* FSM.dot_node_attrs: color from self.dot_node_color.

*Release 20220918*:
Replace callback exception warning() with exception() for the traceback.

*Release 20220805.1*:
* FSM: subclass DOTNodeMixin and provide a hook for a colour palette for node fillcolors.
* Other minor changes.

*Release 20220805*:
Initial PyPI release.

