magicbot: Add tunable update listener method

This adds a way to add a callback for NT updates to tunables.

Author: auscompgeek

magicbot/magic_tunable.py

@@ -1,7 +1,7 @@
 import functools
 import inspect
 import warnings
-from typing import Generic, Optional, TypeVar
+from typing import Callable, Generic, Optional, TypeVar
 
 from networktables import NetworkTables
 from ntcore.value import Value
@@ -67,6 +67,7 @@ def execute(self):
         # "__doc__",
         "_mkv",
         "_nt",
+        "_update_cb",
     )
 
     def __init__(
@@ -87,16 +88,35 @@ def __init__(
 
         self._mkv = Value.getFactory(default)
         self._nt = NetworkTables
+        self._update_cb = None
 
     def __get__(self, instance, owner) -> V:
         if instance is not None:
             return instance._tunables[self].value
         return self
 
-    def __set__(self, instance, value) -> None:
+    def __set__(self, instance, value: V) -> None:
         v = instance._tunables[self]
         self._nt._api.setEntryValueById(v._local_id, self._mkv(value))
 
+    def set_callback(self, callback: Callable[[V], None]) -> None:
+        """
+        Set a method to be called when the tunable is updated over NetworkTables.
+
+        This can be useful, for example, for changing PID gains on a
+        motor controller on the fly::
+
+            class Component:
+                pid: ...
+
+                kP = tunable(0.01)
+
+                @kP.set_callback
+                def set_kP(self, value: float) -> None:
+                    self.pid.setP(value)
+        """
+        self._update_cb = lambda inst, notif: callback(inst, notif.value.value)
+
 
 def setup_tunables(component, cname: str, prefix: Optional[str] = "components") -> None:
     """
@@ -137,6 +157,13 @@ def setup_tunables(component, cname: str, prefix: Optional[str] = "components")
         )
         tunables[prop] = ntvalue
 
+        if prop._update_cb:
+            prop._nt._api.addEntryListenerById(
+                ntvalue._local_id,
+                functools.partial(prop._update_cb, component),
+                NetworkTables.NotifyFlags.UPDATE,
+            )
+
     component._tunables = tunables