From 52124a49eb2492e223b532df91b44c2af1d370d9 Mon Sep 17 00:00:00 2001
From: Vighnesh Birodkar <vighneshbirodkar@gmail.com>
Date: Sun, 14 Dec 2014 06:29:08 +0530
Subject: [PATCH] for iterator change

---
 skimage/graph/graph_merge.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/skimage/graph/graph_merge.py b/skimage/graph/graph_merge.py
index d101cd60..5d918e29 100644
--- a/skimage/graph/graph_merge.py
+++ b/skimage/graph/graph_merge.py
@@ -99,7 +99,7 @@ def merge_hierarchical(labels, rag, thresh, rag_copy, in_place_merge,
         # Reference to the heap item in the graph
         data['heap item'] = heap_item
 
-    while edge_heap[0][0] < thresh:
+    while len(edge_heap) > 0 and edge_heap[0][0] < thresh:
         _, n1, n2, valid = heapq.heappop(edge_heap)
 
         # Ensure popped edge is valid, if not, the edge is discarded