Added instance id as property of base class

sciunit/base.py

@@ -108,6 +108,10 @@ def json(self, add_props=False, keys=None, exclude=None, string=True,
             result = json.loads(result)
         return result
 
+    @property
+    def _id(self):
+        return id(self)
+
     @property
     def _class(self):
         url = getattr(self.__class__,'remote_url','')
@@ -146,7 +150,8 @@ def default(self, obj):
             o = obj._state(state=state, keys=self.keys, exclude=self.exclude)
         elif isinstance(obj,(dict,list,tuple,str,type(None),bool,float,int)):
             o = json.JSONEncoder.default(self, obj)
-        else: # Something we don't know how to serialize; just represent it as truncated string
+        else: # Something we don't know how to serialize; 
+              # just represent it as truncated string
             o = "%.20s..." % obj
         return o
 
@@ -168,6 +173,7 @@ def weights(self):
             weights = [1.0/n for i in range(n)]
         return weights
 
+
 def deep_exclude(state, exclude):
     tuples = [key for key in exclude if isinstance(key,tuple)]
     s = state