Basic Finite State Machine (FSM) tools.

Latest release 20220805: Initial PyPI release.

Class FSM

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, *, history=None, lock=None, transitions=None): Initialise the FSM from:

• state: the initial state
• 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

Class FSMError(builtins.Exception, builtins.BaseException)

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)

Method FSMTransitionEvent.__new__(_cls, old_state, new_state, event, when, extra): Create new instance of FSMTransitionEvent(old_state, new_state, event, when, extra)

Release Log

Release 20220805: Initial PyPI release.