trig serializer wasn't including a @Prefix line for the first graph's…

… prefix

rdflib/plugins/serializers/trig.py

@@ -32,6 +32,7 @@ def __init__(self, store):
     def preprocess(self):
         for context in self.contexts:
             self.store = context
+            self.getQName(context.identifier)
             self._references = defaultdict(int)
             self._subjects = {}
 
@@ -40,22 +41,6 @@ def preprocess(self):
 
             self._contexts[context]=(self.orderSubjects(), self._subjects, self._references)
 
-
-    def preprocessTriple(self, triple):
-        s, p, o = triple
-        self._references[o]+=1
-        self._subjects[s] = True
-        for i, node in enumerate(triple):
-            if node in self.keywords:
-                continue
-            # Don't use generated prefixes for subjects and objects
-            self.getQName(node, gen_prefix=(i == VERB))
-            if isinstance(node, Literal) and node.datatype:
-                self.getQName(node.datatype, gen_prefix=_GEN_QNAME_FOR_DT)
-        p = triple[1]
-        if isinstance(p, BNode):
-            self._references[p]+=1
-
     def reset(self):
         super(TrigSerializer, self).reset()
         self._contexts = {}

test/test_trig.py

@@ -46,3 +46,18 @@ def testSameSubject(self):
         self.assertEqual(len(re.findall(b("p2"), s)), 1)
 
         self.assert_(b('{}') not in s) # no empty graphs!
+
+    def testRememberNamespace(self):
+        g = rdflib.ConjunctiveGraph()
+        g.add((rdflib.URIRef("http://example.com/s"),
+               rdflib.RDFS.label,
+               rdflib.Literal("example 1"),
+               rdflib.URIRef("http://example.com/graph1")))
+        # In 4.2.0 the first serialization would fail to include the
+        # prefix for the graph but later serialize() calls would work.
+        first_out = g.serialize(format='trig')
+        second_out = g.serialize(format='trig')
+        self.assertIn('@prefix ns1: <http://example.com/> .', second_out)
+        self.assertIn('@prefix ns1: <http://example.com/> .', first_out)
+
+        print first_out