Optimize remove_unreachable_nodes in gensim.summarization (#2263)

* slightly optimize remove_unreachable_nodes

* add test

gensim/summarization/commons.py

@@ -63,5 +63,5 @@ def remove_unreachable_nodes(graph):
     """
 
     for node in graph.nodes():
-        if sum(graph.edge_weight((node, other)) for other in graph.neighbors(node)) == 0:
+        if all(graph.edge_weight((node, other)) == 0 for other in graph.neighbors(node)):
             graph.del_node(node)

gensim/test/test_summarization.py

@@ -19,6 +19,30 @@
 from gensim import utils
 from gensim.corpora import Dictionary
 from gensim.summarization import summarize, summarize_corpus, keywords, mz_keywords
+from gensim.summarization.commons import remove_unreachable_nodes, build_graph
+
+
+class TestCommons(unittest.TestCase):
+
+    def _build_graph(self):
+        graph = build_graph(['a', 'b', 'c', 'd'])
+        graph.add_edge(('a', 'b'))
+        graph.add_edge(('b', 'c'))
+        graph.add_edge(('c', 'a'))
+        return graph
+
+    def test_remove_unreachable_nodes(self):
+        graph = self._build_graph()
+        self.assertTrue(graph.has_node('d'))
+        remove_unreachable_nodes(graph)
+        self.assertFalse(graph.has_node('d'))
+
+        graph = self._build_graph()
+        graph.add_edge(('d', 'a'), wt=0.0)
+        graph.add_edge(('b', 'd'), wt=0)
+        self.assertTrue(graph.has_node('d'))
+        remove_unreachable_nodes(graph)
+        self.assertFalse(graph.has_node('d'))
 
 
 class TestSummarizationTest(unittest.TestCase):