Overview

Caution

This section explains how to work with programmatically created state machines. Please note that this is an advanced feature and is usually not necessary to use. You can create state machines much easier using the state machine manager and furthermore use them when you programmatically create projects.

PERSEUS has its own implementation of a state machine, available in perseus.state_machine. Every project holds its own state machine, which allows for fully customizable project workflows for every single project.

The states inside a state machine are represented by a string id which connects to a specific state in the custom states directory.

To describe the behavior of a state machine, you need to define a path. A path can contain three different elements:

• A single state, represented by the id and possibly a condition
• A choice, which holds multiple paths where one is selected based on the conditions
• A fork, which holds multiple paths where all paths are processed simultaneously

To allow for state transitions, states can fire events, possibly containing one or more values to match conditions.

To save a state machine in the database, PERSEUS provides a JSON encoder as well as a JSON decoder:

import json
from perseus.state_machine.StateMachine import StateMachine
from perseus.state_machine.StateMachineJSONDecoder import StateMachineJSONDecoder
from perseus.state_machine.StateMachineJSONEncoder import StateMachineJSONEncoder
...

state_machine: StateMachine = StateMachine(...)
state_machine_json: str = json.dumps(state_machine, cls=StateMachineJSONEncoder)

another_state_machine: StateMachine = json.loads(state_machine_json, cls=StateMachineJSONDecoder)

Please notice the following limitations necessary to ensure a proper working state machine:

• Paths, choices and forks MUST contain at least one element
• Choices and forks SHOULD contain two or more elements
• The first element of a path MUST be a state
• The first element in the top-level path of a state machine MUST NOT have any condition other than None
• The first elements in paths of a fork MUST NOT have any condition other than None
• The first elements in paths of a choice MUST NOT overlap and MUST be unique
• Choices and forks MUST NOT have any condition other than None themselves
• Choices and / or forks MUST have a state in between them and MUST NOT be connected directly