Use a descriptor for DynamicState.fetch_attribute

CHANGELOG

@@ -1,3 +1,5 @@
+0.0.5 Use a descriptor for DynamicState.fetch_attribute to avoid conflicts.
+
 0.0.4 Added signalslot.contrib.dynamic_state.
 
 0.0.3 Removed signal.connect_once(), simplified the code and improved

signalslot/__init__.py

@@ -1,4 +1,4 @@
 from .signal import Signal
 from .exceptions import *
 
-__version__ = '0.0.4'
+__version__ = '0.0.5'

signalslot/contrib/dynamic_state.py

@@ -1,6 +1,12 @@
+
 from signalslot import Signal
 
 
+class DynamicStateSignalDescriptor(property):
+    def __get__(self, cls, owner):
+        return self.fget.__get__(None, owner)()
+
+
 class DynamicState(object):
     """
     Base class for classes which require having dynamic states.
@@ -45,8 +51,6 @@ class DynamicState(object):
     >>> with pytest.raises(AttributeError):
     ...     test.oops
     """
-    fetch_attribute = Signal(args=['obj', 'name'])
-
     def __getattr__(self, name):
         if name not in self.__dict__:
             result = self.fetch_attribute.emit(obj=self, name=name)
@@ -57,3 +61,51 @@ def __getattr__(self, name):
                 raise AttributeError
 
         return getattr(self, name)
+
+    @classmethod
+    def get_fetch_attribute(cls):
+        """
+        Using a property descriptor, we ensure that each DynamicState subclass
+        has its own signal.
+
+        >>> class YourObject(DynamicState):
+        ...     pass
+        ...
+        >>> class YourData(DynamicState):
+        ...     pass
+        ...
+        >>> def fetch_yourobject_foo(obj, name, **kwargs):
+        ...     if name != 'foo':
+        ...         return  # not my responsability
+        ...     return 'yourobject foo'
+        ...
+        >>> def fetch_yourobject_data(obj, name, **kwargs):
+        ...     if name != 'data':
+        ...         return  # not my responsability
+        ...     return YourData()
+        ...
+        >>> def fetch_yourdata_foo(obj, name, **kwargs):
+        ...     if name != 'foo':
+        ...         return  # not my responsability
+        ...     return 'yourdata foo'
+        ...
+        >>> YourObject.fetch_attribute.connect(fetch_yourobject_foo)
+        >>> YourObject.fetch_attribute.connect(fetch_yourobject_data)
+        >>> YourData.fetch_attribute.connect(fetch_yourdata_foo)
+        >>> your_object = YourObject()
+        >>> assert your_object.foo == 'yourobject foo'
+        >>> assert your_object.data.foo == 'yourdata foo'
+        """
+        fetch_attribute = getattr(cls, '_fetch_attribute', None)
+
+        if fetch_attribute is None:
+            cls._fetch_attribute = Signal(args=['obj', 'name'])
+
+        return cls._fetch_attribute
+
+    @classmethod
+    def set_fetch_attribute(cls, value):
+        cls._fetch_attribute = value
+
+    fetch_attribute = DynamicStateSignalDescriptor(get_fetch_attribute,
+                                                   set_fetch_attribute)