Update inference.py

Author: luotao1

python/paddle/v2/inference.py

@@ -37,16 +37,15 @@ def __reader_impl__():
         self.__gradient_machine__.finish()
 
     def iter_infer_field(self, field, **kwargs):
-        for result in self.iter_infer(**kwargs):
-            yield [
-                each_result[each_field]
-                for each_result in result for each_field in field
-            ]
-
-    def infer(self, field='value', **kwargs):
         if not isinstance(field, list) and not isinstance(field, tuple):
             field = [field]
 
+        for result in self.iter_infer(**kwargs):
+            for each_result in result:
+                item = [each_result[each_field] for each_field in field]
+                yield item
+
+    def infer(self, field='value', **kwargs):
         retv = None
         for result in self.iter_infer_field(field=field, **kwargs):
             if retv is None: