[decorators] finally-style decorators and idioms

.vscode/settings.json

@@ -12,10 +12,15 @@
         "behaviours",
         "bierner",
         "bungcip",
+        "epilog",
+        "graphviz",
+        "literalinclude",
+        "noodly",
         "omnilib",
         "py_trees",
         "pydot",
         "pypi",
+        "seealso",
         "ufmt",
         "usort"
     ]

CHANGELOG.rst

@@ -3,7 +3,7 @@ Release Notes
 
 Forthcoming
 -----------
-* ...
+* [decorators] finally-style decorators and idioms, `#427 <https://github.com/splintered-reality/py_trees/pull/427>`_
 
 2.2.3 (2023-02-08)
 ------------------

docs/demos.rst

@@ -147,6 +147,22 @@ py-trees-demo-eternal-guard
    :linenos:
    :caption: py_trees/demos/eternal_guard.py
 
+.. _py-trees-demo-eventually-program:
+
+py-trees-demo-eventually
+------------------------
+
+.. automodule:: py_trees.demos.eventually
+    :members:
+    :special-members:
+    :show-inheritance:
+    :synopsis: demo the finally-like decorator
+
+.. literalinclude:: ../py_trees/demos/eventually.py
+   :language: python
+   :linenos:
+   :caption: py_trees/demos/eventually.py
+
 .. _py-trees-demo-logging-program:
 
 py-trees-demo-logging

docs/dot/demo-eventually.dot

@@ -0,0 +1,17 @@
+digraph pastafarianism {
+ordering=out;
+graph [fontname="times-roman"];
+node [fontname="times-roman"];
+edge [fontname="times-roman"];
+root [fillcolor=orange, fontcolor=black, fontsize=9, label="Ⓜ root", shape=box, style=filled];
+SetFlagFalse [fillcolor=gray, fontcolor=black, fontsize=9, label=SetFlagFalse, shape=ellipse, style=filled];
+root -> SetFlagFalse;
+Parallel [fillcolor=gold, fontcolor=black, fontsize=9, label="Parallel\nSuccessOnOne", shape=parallelogram, style=filled];
+root -> Parallel;
+Counter [fillcolor=gray, fontcolor=black, fontsize=9, label=Counter, shape=ellipse, style=filled];
+Parallel -> Counter;
+Eventually [fillcolor=ghostwhite, fontcolor=black, fontsize=9, label=Eventually, shape=ellipse, style=filled];
+Parallel -> Eventually;
+SetFlagTrue [fillcolor=gray, fontcolor=black, fontsize=9, label=SetFlagTrue, shape=ellipse, style=filled];
+Eventually -> SetFlagTrue;
+}

docs/dot/demo-finally-single-tick.dot

@@ -0,0 +1,17 @@
+digraph pastafarianism {
+ordering=out;
+graph [fontname="times-roman"];
+node [fontname="times-roman"];
+edge [fontname="times-roman"];
+root [fillcolor=orange, fontcolor=black, fontsize=9, label="Ⓜ root", shape=box, style=filled];
+SetFlagFalse [fillcolor=gray, fontcolor=black, fontsize=9, label=SetFlagFalse, shape=ellipse, style=filled];
+root -> SetFlagFalse;
+Parallel [fillcolor=gold, fontcolor=black, fontsize=9, label="Parallel\nSuccessOnOne", shape=parallelogram, style=filled];
+root -> Parallel;
+Counter [fillcolor=gray, fontcolor=black, fontsize=9, label=Counter, shape=ellipse, style=filled];
+Parallel -> Counter;
+Finally [fillcolor=ghostwhite, fontcolor=black, fontsize=9, label=Finally, shape=ellipse, style=filled];
+Parallel -> Finally;
+SetFlagTrue [fillcolor=gray, fontcolor=black, fontsize=9, label=SetFlagTrue, shape=ellipse, style=filled];
+Finally -> SetFlagTrue;
+}

docs/dot/eventually.dot

@@ -0,0 +1,17 @@
+digraph pastafarianism {
+ordering=out;
+graph [fontname="times-roman"];
+node [fontname="times-roman"];
+edge [fontname="times-roman"];
+Parallel [fillcolor=gold, fontcolor=black, fontsize=9, label="Parallel\nSuccessOnOne", shape=parallelogram, style=filled];
+Worker [fillcolor=orange, fontcolor=black, fontsize=9, label="Ⓜ Worker", shape=box, style=filled];
+Parallel -> Worker;
+Glory [fillcolor=gray, fontcolor=black, fontsize=9, label=Glory, shape=ellipse, style=filled];
+Worker -> Glory;
+Infamy [fillcolor=gray, fontcolor=black, fontsize=9, label=Infamy, shape=ellipse, style=filled];
+Worker -> Infamy;
+Eventually [fillcolor=ghostwhite, fontcolor=black, fontsize=9, label=Eventually, shape=ellipse, style=filled];
+Parallel -> Eventually;
+Colander [fillcolor=gray, fontcolor=black, fontsize=9, label=Colander, shape=ellipse, style=filled];
+Eventually -> Colander;
+}

docs/examples/eventually.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+import py_trees
+
+if __name__ == "__main__":
+    root = py_trees
+    task_one = py_trees.behaviours.StatusQueue(
+        name="Glory",
+        queue=[
+            py_trees.common.Status.RUNNING,
+        ],
+        eventually=py_trees.common.Status.SUCCESS,
+    )
+    task_two = py_trees.behaviours.Success(name="Infamy")
+    worker = py_trees.composites.Sequence(
+        name="Worker", memory=True, children=[task_one, task_two]
+    )
+    root = py_trees.idioms.eventually(
+        name="Parallel",
+        worker=worker,
+        eventually=py_trees.behaviours.Success("Colander"),
+    )
+    py_trees.display.render_dot_tree(
+        root, py_trees.common.string_to_visibility_level("all")
+    )

py_trees/behaviour.py

@@ -344,7 +344,7 @@ def iterate(self, direct_descendants: bool = False) -> typing.Iterator[Behaviour
                 yield child
         yield self
 
-    # TODO: better type refinement of 'viso=itor'
+    # TODO: better type refinement of 'visitor'
     def visit(self, visitor: typing.Any) -> None:
         """
         Introspect on this behaviour with a visitor.

py_trees/behaviours.py

@@ -280,6 +280,7 @@ def update(self) -> common.Status:
             :data:`~py_trees.common.Status.RUNNING` while not expired, the given completion status otherwise
         """
         self.counter += 1
+        self.feedback_message = f"count: {self.counter}"
         if self.counter <= self.duration:
             return common.Status.RUNNING
         else:

py_trees/decorators.py

@@ -38,6 +38,7 @@
 * :class:`py_trees.decorators.EternalGuard`
 * :class:`py_trees.decorators.Inverter`
 * :class:`py_trees.decorators.OneShot`
+* :class:`py_trees.decorators.OnTerminate`
 * :class:`py_trees.decorators.Repeat`
 * :class:`py_trees.decorators.Retry`
 * :class:`py_trees.decorators.StatusToBlackboard`
@@ -920,3 +921,79 @@ def update(self) -> common.Status:
             the behaviour's new status :class:`~py_trees.common.Status`
         """
         return self.decorated.status
+
+
+class OnTerminate(Decorator):
+    """
+    Trigger the child for a single tick on :meth:`terminate`.
+
+    Always return :data:`~py_trees.common.Status.RUNNING` and on
+    on :meth:`terminate`, call the child's
+    :meth:`~py_trees.behaviour.Behaviour.update` method, once.
+
+    This is useful to cleanup, restore a context switch or to
+    implement a finally-like behaviour.
+
+    .. seealso:: :meth:`py_trees.idioms.eventually`
+
+    NB: If you need to persist the execution of the 'finally'-like block for more
+    than a single tick, you'll need to build that explicitly into your tree. There
+    are various ways of doing so (with and without the blackboard). One pattern
+    that works:
+
+    .. code-block::
+
+        [o] Selector
+            {-} Sequence
+                --> Work
+                --> Finally (Triggers on Success)
+            {-} Sequence
+                --> Finally (Triggers on Failure)
+                --> Failure
+    """
+
+    def __init__(self, name: str, child: behaviour.Behaviour):
+        """
+        Initialise with the standard decorator arguments.
+
+        Args:
+            name: the decorator name
+            child: the child to be decorated
+        """
+        super(OnTerminate, self).__init__(name=name, child=child)
+
+    def tick(self) -> typing.Iterator[behaviour.Behaviour]:
+        """
+        Bypass the child when ticking.
+
+        Yields:
+            a reference to itself
+        """
+        self.logger.debug(f"{self.__class__.__name__}.tick()")
+        self.status = self.update()
+        yield self
+
+    def update(self):
+        """
+        Return with :data:`~py_trees.common.Status.RUNNING`.
+
+        Returns:
+            the behaviour's new status :class:`~py_trees.common.Status`
+        """
+        return common.Status.RUNNING
+
+    def terminate(self, new_status: common.Status) -> None:
+        """Tick the child behaviour once."""
+        self.logger.debug(
+            "{}.terminate({})".format(
+                self.__class__.__name__,
+                "{}->{}".format(self.status, new_status)
+                if self.status != new_status
+                else f"{new_status}",
+            )
+        )
+        if new_status == common.Status.INVALID:
+            self.decorated.tick_once()
+            # Do not need to stop the child here - this method
+            # is only called by Decorator.stop() which will handle
+            # that responsibility immediately after this method returns.

py_trees/demos/__init__.py

@@ -21,6 +21,7 @@
 from . import display_modes  # usort:skip  # noqa: F401
 from . import dot_graphs  # usort:skip  # noqa: F401
 from . import either_or  # usort:skip  # noqa: F401
+from . import eventually  # usort:skip  # noqa: F401
 from . import lifecycle  # usort:skip  # noqa: F401
 from . import selector  # usort:skip  # noqa: F401
 from . import sequence  # usort:skip  # noqa: F401