Add an option to make the effect of sync_attr and sync_attrs permanent

src/asynckivy/_utils.py

@@ -147,20 +147,29 @@ def __exit__(self, *args):
 
 class sync_attr:
     '''
-    Returns a context manager that creates one-directional binding between attributes.
+    Creates one-directional binding between attributes.
 
     .. code-block::
 
         import types
 
-        widget = Widget()
+        widget = Widget(x=100)
         obj = types.SimpleNamespace()
 
-        with sync_attr(from_=(widget, 'x'), to_=(obj, 'xx')):
-            widget.x = 10
-            assert obj.xx == 10  # synchronized
-            obj.xx = 20
-            assert widget.x == 10  # but not the other way around
+        sync_attr(from_=(widget, 'x'), to_=(obj, 'xx')):
+        assert obj.xx == 100  # synchronized
+        widget.x = 10
+        assert obj.xx == 10  # synchronized
+        obj.xx = 20
+        assert widget.x == 10  # but not the other way around
+
+    To make its effect temporary, use it with a with-statement:
+
+    .. code-block::
+
+        # The effect lasts only within the with-block.
+        with sync_attr(...):
+            ...
 
     This can be particularly useful when combined with :func:`transform`.
 
@@ -169,7 +178,7 @@ class sync_attr:
         from kivy.graphics import Rotate
 
         async def rotate_widget(widget, *, angle=360.):
-            rotate = Rotate(origin=widget.center)
+            rotate = Rotate()
             with (
                 transform(widget) as ig,
                 sync_attr(from_=(widget, 'center'), to_=(rotate, 'origin')),
@@ -178,23 +187,35 @@ async def rotate_widget(widget, *, angle=360.):
                 await anim_attrs(rotate, angle=angle)
 
     .. versionadded:: 0.6.1
+
+    .. versionchanged:: 0.8.0
+        The context manager now applies its effect upon creation, rather than when its ``__enter__()`` method is
+        called, and ``__enter__()`` no longer performs any action.
+
+        Additionally, the context manager now assigns the ``from_`` value to the ``to_`` upon creation:
+
+        .. code-block::
+
+            with sync_attr((widget, 'x'), (obj, 'xx')):
+                assert widget.x == obj.xx
     '''
-    __slots__ = ('_from', '_to', '_bind_uid', )
+    __slots__ = ("__exit__", )
 
-    def __init__(self, from_: T.Tuple[EventDispatcher, str], to_: T.Tuple[T.Any, str]):
-        self._from = from_
-        self._to = to_
+    def __init__(self, from_: tuple[EventDispatcher, str], to_: tuple[T.Any, str]):
+        setattr(*to_, getattr(*from_))
+        bind_uid = from_[0].fbind(from_[1], partial(self._sync, setattr, *to_))
+        self.__exit__ = partial(self._unbind, *from_, bind_uid)
 
+    @staticmethod
     def _sync(setattr, obj, attr_name, event_dispatcher, new_value):
         setattr(obj, attr_name, new_value)
 
-    def __enter__(self, partial=partial, sync=partial(_sync, setattr)):
-        self._bind_uid = self._from[0].fbind(self._from[1], partial(sync, *self._to))
+    @staticmethod
+    def _unbind(event_dispatcher, event_name, bind_uid, *__):
+        event_dispatcher.unbind_uid(event_name, bind_uid)
 
-    def __exit__(self, *args):
-        self._from[0].unbind_uid(self._from[1], self._bind_uid)
-
-    del _sync
+    def __enter__(self):
+        pass
 
 
 class sync_attrs:
@@ -221,8 +242,8 @@ class sync_attrs:
         from kivy.graphics import Rotate, Scale
 
         async def scale_and_rotate_widget(widget, *, scale=2.0, angle=360.):
-            rotate = Rotate(origin=widget.center)
-            scale = Scale(origin=widget.center)
+            rotate = Rotate()
+            scale = Scale()
             with (
                 transform(widget) as ig,
                 sync_attrs((widget, 'center'), (rotate, 'origin'), (scale, 'origin')),
@@ -235,21 +256,32 @@ async def scale_and_rotate_widget(widget, *, scale=2.0, angle=360.):
                 )
 
     .. versionadded:: 0.6.1
+
+    .. versionchanged:: 0.8.0
+        The context manager now applies its effect upon creation, rather than when its ``__enter__()`` method is
+        called, and ``__enter__()`` no longer performs any action.
+
+        Additionally, the context manager now assigns the ``from_`` value to the ``to_`` upon creation:
+
+        .. code-block::
+
+            with sync_attrs((widget, 'x'), (obj, 'xx')):
+                assert widget.x is obj.xx
     '''
-    __slots__ = ('_from', '_to', '_bind_uid', )
+    __slots__ = ("__exit__", )
 
-    def __init__(self, from_: T.Tuple[EventDispatcher, str], *to_):
-        self._from = from_
-        self._to = to_
+    def __init__(self, from_: tuple[EventDispatcher, str], *to_):
+        sync = partial(self._sync, setattr, to_)
+        sync(None, getattr(*from_))
+        bind_uid = from_[0].fbind(from_[1], sync)
+        self.__exit__ = partial(self._unbind, *from_, bind_uid)
 
+    @staticmethod
     def _sync(setattr, to_, event_dispatcher, new_value):
         for obj, attr_name in to_:
             setattr(obj, attr_name, new_value)
 
-    def __enter__(self, partial=partial, sync=partial(_sync, setattr)):
-        self._bind_uid = self._from[0].fbind(self._from[1], partial(sync, self._to))
-
-    def __exit__(self, *args):
-        self._from[0].unbind_uid(self._from[1], self._bind_uid)
+    _unbind = staticmethod(sync_attr._unbind)
 
-    del _sync
+    def __enter__(self):
+        pass

tests/test_utils_sync_attr.py

@@ -7,7 +7,7 @@ def human_cls():
     from kivy.properties import NumericProperty
 
     class Human(EventDispatcher):
-        age = NumericProperty()
+        age = NumericProperty(10)
 
     return Human
 
@@ -23,6 +23,7 @@ def test_sync_attr(human):
 
     obj = types.SimpleNamespace()
     with ak.sync_attr(from_=(human, 'age'), to_=(obj, 'AGE')):
+        assert obj.AGE == 10
         human.age = 2
         assert obj.AGE == 2
         human.age = 0
@@ -37,6 +38,8 @@ def test_sync_attrs(human):
 
     obj = types.SimpleNamespace()
     with ak.sync_attrs((human, 'age'), (obj, 'AGE'), (obj, 'age')):
+        assert obj.AGE == 10
+        assert obj.age == 10
         human.age = 2
         assert obj.AGE == 2
         assert obj.age == 2