Super State Machine

Super State Machine gives you utilities to build finite state machines.

• Free software: BSD license
• Documentation: https://super_state_machine.readthedocs.org
• Source: https://github.com/beregond/super_state_machine

Features

• Fully tested with Python 2.7, 3.3, 3.4 and PyPy.

• Create finite state machines:

  >>> from enum import Enum
  >>> from super_state_machine import machines
  
  >>> class Task(machines.StateMachine):
  ...
  ...    state = 'draft'
  ...
  ...    class States(Enum):
  ...
  ...         DRAFT = 'draft'
  ...         SCHEDULED = 'scheduled'
  ...         PROCESSING = 'processing'
  ...         SENT = 'sent'
  ...         FAILED = 'failed'
  
  >>> task = Task()
  >>> task.is_draft
  False
  >>> task.set_draft()
  >>> task.state
  'draft'
  >>> task.state = 'scheduled'
  >>> task.is_scheduled
  True
  >>> task.state = 'process'
  >>> task.state
  'processing'
  >>> task.state = 'wrong'
  *** ValueError: Unrecognized value ('wrong').

• Define allowed transitions graph, define additional named transitions and checkers:

  >>> class Task(machines.StateMachine):
  ...
  ...     class States(Enum):
  ...
  ...         DRAFT = 'draft'
  ...         SCHEDULED = 'scheduled'
  ...         PROCESSING = 'processing'
  ...         SENT = 'sent'
  ...         FAILED = 'failed'
  ...
  ...     class Meta:
  ...
  ...         allow_empty = False
  ...         initial_state = 'draft'
  ...         transitions = {
  ...             'draft': ['scheduled', 'failed'],
  ...             'scheduled': ['failed'],
  ...             'processing': ['sent', 'failed']
  ...         }
  ...         named_transitions = [
  ...             ('process', 'processing', ['scheduled']),
  ...             ('fail', 'failed')
  ...         ]
  ...         named_checkers = [
  ...             ('can_be_processed', 'processing'),
  ...         ]
  
  >>> task = Task()
  >>> task.state
  'draft'
  >>> task.process()
  *** TransitionError: Cannot transit from 'draft' to 'processing'.
  >>> task.set_scheduled()
  >>> task.can_be_processed
  True
  >>> task.process()
  >>> task.state
  'processing'
  >>> task.fail()
  >>> task.state
  'failed'

Note, that third argument restricts from which states transition will be added to allowed (in case of process, new allowed transition will be added, from 'scheduled' to 'processing'). No argument means all available states, None or empty list won't add anything beyond defined ones.

• Use state machines as properties:

  >>> from enum import Enum
  >>> from super_state_machine import machines, extras
  
  
  >>> class Lock(machines.StateMachine):
  
  ...     class States(Enum):
  ...
  ...         OPEN = 'open'
  ...         LOCKED = 'locked'
  ...
  ...     class Meta:
  ...
  ...         allow_empty = False
  ...         initial_state = 'locked'
  ...         named_transitions = [
  ...             ('open', 'open'),
  ...             ('lock', 'locked'),
  ...         ]
  
  
  >>> class Safe(object):
  ...
  ...     lock1 = extras.PropertyMachine(Lock)
  ...     lock2 = extras.PropertyMachine(Lock)
  ...     lock3 = extras.PropertyMachine(Lock)
  ...
  ...     locks = ['lock1', 'lock2', 'lock3']
  ...
  ...     def is_locked(self):
  ...          locks = [getattr(self, lock).is_locked for lock in self.locks]
  ...          return any(locks)
  ...
  ...     def is_open(self):
  ...         locks = [getattr(self, lock).is_open for lock in self.locks]
  ...         return all(locks)
  
  >>> safe = Safe()
  >>> safe.lock1
  'locked'
  >>> safe.is_open
  False
  >>> safe.lock1.open()
  >>> safe.lock1.is_open
  True
  >>> safe.lock1
  'open'
  >>> safe.is_open
  False
  >>> safe.lock2.open()
  >>> safe.lock3 = 'open'
  >>> safe.is_open
  True