BUG: fix python 3 dtype issue

Author: wesm

pandas/io/parsers.py

@@ -826,11 +826,13 @@ def _convert_types(self, values, na_values, try_num_bool=True):
             try:
                 result = lib.maybe_convert_numeric(values, na_values, False)
             except Exception:
-                na_count = lib.sanitize_objects(values, na_values, False)
                 result = values
+                if values.dtype == np.object_:
+                    na_count = lib.sanitize_objects(result, na_values, False)
         else:
-            na_count = lib.sanitize_objects(values, na_values, False)
             result = values
+            if values.dtype == np.object_:
+                na_count = lib.sanitize_objects(values, na_values, False)
 
         if result.dtype == np.object_ and try_num_bool:
             result = lib.maybe_convert_bool(values,