diff --git a/DataCollection.py b/DataCollection.py
index ef95130..03100cf 100644
--- a/DataCollection.py
+++ b/DataCollection.py
@@ -578,6 +578,9 @@ def invokeGenerator(self):
     
     def generatorFunction(self):
         
+        if self.generator.isEmpty():
+            raise Exception("DataCollection.generatorFunction: generator called with insufficient samples.")
+        
         while(not self.generator.isEmpty()):
 
             data = self.generator.getBatch()
@@ -592,6 +595,6 @@ def generatorFunction(self):
                 out = (xout,yout,wout)
             yield out
             
-        raise Exception("DataCollection.generatorFunction: generator ran out of samples. This should not have happened, please report bug.")
+        
         
     
diff --git a/bin/convertFromSource.py b/bin/convertFromSource.py
index 3a985d2..082bc96 100755
--- a/bin/convertFromSource.py
+++ b/bin/convertFromSource.py
@@ -104,9 +104,9 @@
 traind=None
 if class_name in class_options:
     traind = class_options[class_name]
-elif not recover and not testdatafor:
+elif not recover:
     print('available classes:')
-    for key, val in class_options.iteritems():
+    for key, val in class_options.items():
         print(key)
     raise Exception('wrong class selection')
 
diff --git a/bin/mergeDataCollections.py b/bin/mergeDataCollections.py
index 7b96d32..5e98bcc 100755
--- a/bin/mergeDataCollections.py
+++ b/bin/mergeDataCollections.py
@@ -1,4 +1,4 @@
-#! /bin/env python3
+#!/bin/env python3
 
 from argparse import ArgumentParser
 from DeepJetCore.DataCollection import DataCollection