BUG: use pprint_thing() rather then str()

Author: y-p

pandas/core/frame.py

@@ -3915,7 +3915,8 @@ def _apply_standard(self, func, axis, ignore_failures=False):
                 try:
                     if hasattr(e, 'args'):
                         k = res_index[i]
-                        e.args = e.args + ('occurred at index %s' % str(k),)
+                        e.args = e.args + ('occurred at index %s' %
+                                           com.pprint_thing(k),)
                 except (NameError, UnboundLocalError):  # pragma: no cover
                     # no k defined yet
                     pass