Action Trees

Source Code: https://gitlab.com/roxautomation/action-trees

Summary

Action Trees is an asyncio-based Python library for managing hierarchical and asynchronous tasks. It breaks down complex tasks into simpler, independent steps that can be run sequentially or in parallel.

Functionality

• ActionItem Class: Central class for representing tasks, supporting states like INITIALIZING, RUNNING, PAUSED, and FAILED.
• Task Management: Provides APIs to start, pause, resume, and cancel tasks asynchronously.
• Hierarchical Actions: Actions can have child actions, supporting structured, tree-like task management.
• Parallel Execution: Supports running child tasks concurrently using asyncio.
• State and Exception Handling: Handles task state transitions and exceptions, ensuring proper state flow.

Example

The following example illustrates a high-level task to prepare and make a cappuccino using the ActionItem class:

import asyncio
from action_trees import ActionItem

class AtomicAction(ActionItem):
    """Basic machine action with no children."""
    def __init__(self, name: str, duration: float = 0.1):
        super().__init__(name=name)
        self._duration = duration

    async def _on_run(self) -> None:
        await asyncio.sleep(self._duration)

class PrepareMachineAction(ActionItem):
    """Prepare the machine."""
    def __init__(self) -> None:
        super().__init__(name="prepare")
        self.add_child(AtomicAction(name="initialize"))
        self.add_child(AtomicAction(name="clean"))

    async def _on_run(self) -> None:
        for child in self.children:
            await child.start()

class MakeCappuccinoAction(ActionItem):
    """Make cappuccino."""
    def __init__(self) -> None:
        super().__init__(name="make_cappuccino")
        self.add_child(AtomicAction(name="boil_water"))
        self.add_child(AtomicAction(name="grind_coffee"))

    async def _on_run(self) -> None:
        await self.run_children_parallel()

class CappuccinoOrder(ActionItem):
    """High-level action to make a cappuccino."""
    def __init__(self) -> None:
        super().__init__(name="cappuccino_order")
        self.add_child(PrepareMachineAction())
        self.add_child(MakeCappuccinoAction())

    async def _on_run(self) -> None:
        for child in self.children:
            await child.start()

async def main() -> None:
    order = CappuccinoOrder()
    await order.start()
    order.display_tree()

if __name__ == "__main__":
    asyncio.run(main())

This code creates a hierarchical task to prepare a machine and make a cappuccino, with some actions running sequentially and others in parallel.

More examples : see examples

State transitions

ActionItem contains a state machine with these transitions. (spec from VDA5050)