correctly return the length of rdf:List for RDFLib#223

rdflib/collection.py

@@ -82,12 +82,7 @@ def _get_container(self, index):
 
     def __len__(self):
         """length of items in collection."""
-        count = 0
-        links = set()
-        for item in self.graph.items(self.uri):
-            links.add(item)
-            count += 1
-        return count
+        return len(list(self.graph.items(self.uri)))
 
     def index(self, item):
         """

test/test_issue223.py

@@ -11,8 +11,9 @@ def test_collection_with_duplicates():
     g = Graph().parse(data=ttl, format="turtle")
     for _,_,o in g.triples((URIRef("http://example.org/s"), URIRef("http://example.org/p"), None)):
         break
-    c = list(Collection(g, o))
-    assert c == list(URIRef("http://example.org/" + x) for x in ["a", "b", "a"])
-
+    c = Collection(g, o)
+    assert list(c) == list(URIRef("http://example.org/" + x) for x in ["a", "b", "a"])
+    assert len(c) == 3
+
 if __name__ == '__main__':
     test_collection_with_duplicates()