Don't init property created in KV with given value because it is stor…

…ed in the class causing memory leaks.

kivy/_event.pyx

@@ -800,7 +800,7 @@ cdef class EventDispatcher(ObjectWithUid):
             ret[x] = p[x]
         return ret
 
-    def create_property(self, str name, value=None, *largs, **kwargs):
+    def create_property(self, str name, value=None, default_value=True, *largs, **kwargs):
         '''Create a new property at runtime.
 
         .. versionadded:: 1.0.9
@@ -817,6 +817,10 @@ cdef class EventDispatcher(ObjectWithUid):
             Also, now and positional and keyword arguments are passed to the
             property when created.
 
+        .. versionchanged:: 2.0.0
+
+            default_value has been added.
+
         .. warning::
 
             This function is designed for the Kivy language, don't use it in
@@ -829,7 +833,10 @@ cdef class EventDispatcher(ObjectWithUid):
             `value`: object, optional
                 Default value of the property. Type is also used for creating
                 more appropriate property types. Defaults to None.
-
+            `default_value`: bool, True by default
+                If True, `value` will be the default for the property. Otherwise,
+                the property will be initialized with the the property type's
+                normal default value, and subsequently set to ``value``.
 
         ::
 
@@ -840,25 +847,46 @@ cdef class EventDispatcher(ObjectWithUid):
             True
         '''
         cdef Property prop
-        if value is None:  # shortcut
-            prop = ObjectProperty(None, *largs, **kwargs)
-        if isinstance(value, bool):
-            prop = BooleanProperty(value, *largs, **kwargs)
-        elif isinstance(value, (int, float)):
-            prop = NumericProperty(value, *largs, **kwargs)
-        elif isinstance(value, string_types):
-            prop = StringProperty(value, *largs, **kwargs)
-        elif isinstance(value, (list, tuple)):
-            prop = ListProperty(value, *largs, **kwargs)
-        elif isinstance(value, dict):
-            prop = DictProperty(value, *largs, **kwargs)
+
+        if default_value:
+            if value is None:  # shortcut
+                prop = ObjectProperty(None, *largs, **kwargs)
+            if isinstance(value, bool):
+                prop = BooleanProperty(value, *largs, **kwargs)
+            elif isinstance(value, (int, float)):
+                prop = NumericProperty(value, *largs, **kwargs)
+            elif isinstance(value, string_types):
+                prop = StringProperty(value, *largs, **kwargs)
+            elif isinstance(value, (list, tuple)):
+                prop = ListProperty(value, *largs, **kwargs)
+            elif isinstance(value, dict):
+                prop = DictProperty(value, *largs, **kwargs)
+            else:
+                prop = ObjectProperty(value, *largs, **kwargs)
         else:
-            prop = ObjectProperty(value, *largs, **kwargs)
+            if value is None:  # shortcut
+                prop = ObjectProperty(*largs, **kwargs)
+            if isinstance(value, bool):
+                prop = BooleanProperty(*largs, **kwargs)
+            elif isinstance(value, (int, float)):
+                prop = NumericProperty(*largs, **kwargs)
+            elif isinstance(value, string_types):
+                prop = StringProperty(*largs, **kwargs)
+            elif isinstance(value, (list, tuple)):
+                prop = ListProperty(*largs, **kwargs)
+            elif isinstance(value, dict):
+                prop = DictProperty(*largs, **kwargs)
+            else:
+                prop = ObjectProperty(*largs, **kwargs)
+
         prop.link(self, name)
         prop.link_deps(self, name)
         self.__properties[name] = prop
         setattr(self.__class__, name, prop)
 
+        if not default_value:
+            setattr(self, name, value)
+
     def apply_property(self, **kwargs):
         '''Adds properties at runtime to the class. The function accepts
         keyword arguments of the form `prop_name=prop`, where `prop` is a

kivy/lang/parser.py

@@ -281,7 +281,7 @@ def create_missing(self, widget):
             value = self.properties[name].co_value
             if type(value) is CodeType:
                 value = None
-            widget.create_property(name, value)
+            widget.create_property(name, value, default_value=False)
 
     def _forbid_selectors(self):
         c = self.name[0]