1 files changed, 80 insertions, 0 deletions
diff --git a/netlib/stateobject.py b/netlib/stateobject.py
new file mode 100644
index 00000000..c2ef2cd4
--- /dev/null
+++ b/netlib/stateobject.py
@@ -0,0 +1,80 @@
+from types import ClassType
+
+
+class StateObject:
+    def _get_state(self):
+        raise NotImplementedError
+
+    def _load_state(self, state):
+        raise NotImplementedError
+
+    @classmethod
+    def _from_state(cls, state):
+        raise NotImplementedError
+
+    def __eq__(self, other):
+        try:
+            return self._get_state() == other._get_state()
+        except AttributeError:  # we may compare with something that's not a StateObject
+            return False
+
+
+class SimpleStateObject(StateObject):
+    """
+    A StateObject with opionated conventions that tries to keep everything DRY.
+
+    Simply put, you agree on a list of attributes and their type.
+    Attributes can either be primitive types(str, tuple, bool, ...) or StateObject instances themselves.
+    SimpleStateObject uses this information for the default _get_state(), _from_state(s) and _load_state(s) methods.
+    Overriding _get_state or _load_state to add custom adjustments is always possible.
+    """
+
+    _stateobject_attributes = None  # none by default to raise an exception if definition was forgotten
+    """
+    An attribute-name -> class-or-type dict containing all attributes that should be serialized
+    If the attribute is a class, this class must be a subclass of StateObject.
+    """
+
+    def _get_state(self):
+        return {attr: self.__get_state_attr(attr, cls)
+                for attr, cls in self._stateobject_attributes.iteritems()}
+
+    def __get_state_attr(self, attr, cls):
+        """
+        helper for _get_state.
+        returns the value of the given attribute
+        """
+        if getattr(self, attr) is None:
+            return None
+        if isinstance(cls, ClassType):
+            return getattr(self, attr)._get_state()
+        else:
+            return getattr(self, attr)
+
+    def _load_state(self, state):
+        for attr, cls in self._stateobject_attributes.iteritems():
+            self.__load_state_attr(attr, cls, state)
+
+    def __load_state_attr(self, attr, cls, state):
+        """
+        helper for _load_state.
+        loads the given attribute from the state.
+        """
+        if state[attr] is not None:  # First, catch None as value.
+            if isinstance(cls, ClassType):  # Is the attribute a StateObject itself?
+                assert issubclass(cls, StateObject)
+                curr = getattr(self, attr)
+                if curr:  # if the attribute is already present, delegate to the objects ._load_state method.
+                    curr._load_state(state[attr])
+                else: # otherwise, create a new object.
+                    setattr(self, attr, cls._from_state(state[attr]))
+            else:
+                setattr(self, attr, cls(state[attr]))
+        else:
+            setattr(self, attr, None)
+
+    @classmethod
+    def _from_state(cls, state):
+        f = cls()  # the default implementation assumes an empty constructor. Override accordingly.
+        f._load_state(state)
+        return f
+\ No newline at end of file