try out py2 before py3 refactor to make sure correct workflow (#75)

Author: stevenhua0320

Diff for: src/diffpy/srmise/dataclusters.py

@@ -172,7 +172,7 @@ def _setdata(self, x, y, res):
         self.lastcluster_idx = None
         return
 
-    def next(self):
+    def __next__(self):
         """Cluster point with largest y-coordinate left, returning self.
 
         next() always adds at least one additional point to the existing
@@ -217,7 +217,7 @@ def next(self):
             else:
                 # insert right of nearest cluster
                 self.lastcluster_idx = nearest_cluster[0] + 1
-            self.clusters = np.insert(self.clusters, self.lastcluster_idx, [test_idx, test_idx], 0)
+            self.clusters = np.insert(self.clusters, int(self.lastcluster_idx), [test_idx, test_idx], 0)
         return self
 
     def makeclusters(self):
@@ -286,8 +286,8 @@ def find_nearest_cluster(self, idx):
         # Calculate which of the two nearest clusters is closer
         distances = np.array(
             [
-                self.x[idx] - self.x[self.clusters[near_idx - 1, 1]],
-                self.x[idx] - self.x[self.clusters[near_idx, 0]],
+                self.x[idx] - self.x[self.clusters[int(near_idx) - 1, 1]],
+                self.x[idx] - self.x[self.clusters[int(near_idx), 0]],
             ]
         )
         if distances[0] < np.abs(distances[1]):