Fix #436

Permit partial, partialmethod, and wraps to be used with event handlers

gpiozero/mixins.py

@@ -9,7 +9,7 @@ str = type('')
 
 import inspect
 import weakref
-from functools import wraps
+from functools import wraps, partial
 from threading import Event
 from collections import deque
 from time import time
@@ -255,7 +255,16 @@ class EventsMixin(object):
             return None
         elif not callable(fn):
             raise BadEventHandler('value must be None or a callable')
-        elif inspect.isbuiltin(fn):
+        # If fn is wrapped with partial (i.e. partial, partialmethod, or wraps
+        # has been used to produce it) we need to dig out the "real" function
+        # that's been wrapped along with all the mandatory positional args
+        # used in the wrapper so we can test the binding
+        args = ()
+        wrapped_fn = fn
+        while isinstance(wrapped_fn, partial):
+            args = wrapped_fn.args + args
+            wrapped_fn = wrapped_fn.func
+        if inspect.isbuiltin(wrapped_fn):
             # We can't introspect the prototype of builtins. In this case we
             # assume that the builtin has no (mandatory) parameters; this is
             # the most reasonable assumption on the basis that pre-existing
@@ -267,13 +276,13 @@ class EventsMixin(object):
             # If this works, assume the function is capable of accepting no
             # parameters
             try:
-                inspect.getcallargs(fn)
+                inspect.getcallargs(wrapped_fn, *args)
                 return fn
             except TypeError:
                 try:
                     # If the above fails, try binding with a single parameter
                     # (ourselves). If this works, wrap the specified callback
-                    inspect.getcallargs(fn, self)
+                    inspect.getcallargs(wrapped_fn, *(args + (self,)))
                     @wraps(fn)
                     def wrapper():
                         return fn(self)

tests/test_inputs.py

@@ -10,6 +10,7 @@ str = type('')
 import sys
 import pytest
 from threading import Event
+from functools import partial
 
 from gpiozero.pins.mock import (
     MockPin,
@@ -79,6 +80,20 @@ def test_input_event_deactivated():
         pin.drive_low()
         assert event.is_set()
 
+def test_input_partial_callback():
+    event = Event()
+    pin = MockPin(2)
+    def foo(a, b):
+        event.set()
+        return a + b
+    bar = partial(foo, 1)
+    baz = partial(bar, 2)
+    with DigitalInputDevice(pin) as device:
+        device.when_activated = baz
+        assert not event.is_set()
+        pin.drive_high()
+        assert event.is_set()
+
 def test_input_wait_active():
     pin = MockPin(2)
     with DigitalInputDevice(pin) as device: