Fix ZeroDivisionError keywords issue with short input (#2154)

* Return keywords before matrix processing if no graph edges.

* Add testcase for empty graph.

gensim/summarization/keywords.py

@@ -512,6 +512,9 @@ def keywords(text, ratio=0.2, words=None, split=False, scores=False, pos_filter=
 
     _remove_unreachable_nodes(graph)
 
+    if not graph.edges():
+        return _format_results([], [], split, scores)
+
     # Ranks the tokens using the PageRank algorithm. Returns dict of lemma -> score
     pagerank_scores = _pagerank(graph)
 

gensim/test/test_keywords.py

@@ -95,6 +95,12 @@ def test_text_keywords_with_small_graph(self):
         kwds = keywords(text, words=1, split=True)
         self.assertTrue(len(kwds))
 
+    def test_text_keywords_without_graph_edges(self):
+        # regression test, we get graph with no edges on this text
+        text = 'Sitio construcción. Estaremos línea.'
+        kwds = keywords(text, deacc=False, scores=True)
+        self.assertFalse(len(kwds))
+
 
 if __name__ == '__main__':
     logging.basicConfig(format='%(asctime)s : %(levelname)s : %(message)s', level=logging.DEBUG)