Merge pull request #504 from RDFLib/issue-495-graphs-method

Re-added 'graphs' method as alias of 'contexts' to the Dataset object, fixes #495

rdflib/graph.py

@@ -1625,9 +1625,12 @@ def remove_graph(self, g):
     def contexts(self, triple=None):
         default = False
         for c in super(Dataset, self).contexts(triple):
-            default|=c.identifier == DATASET_DEFAULT_GRAPH_ID
+            default |= c.identifier == DATASET_DEFAULT_GRAPH_ID
             yield c
-        if not default: yield self.graph(DATASET_DEFAULT_GRAPH_ID)
+        if not default:
+            yield self.graph(DATASET_DEFAULT_GRAPH_ID)
+
+    graphs = contexts
 
     def quads(self, quad):
         for s, p, o, c in super(Dataset, self).quads(quad):
@@ -1636,7 +1639,6 @@ def quads(self, quad):
             else:
                 yield (s, p, o, c.identifier)
 
-
 class QuotedGraph(Graph):
     """
     Quoted Graphs are intended to implement Notation 3 formulae. They are