diff -r b47996cf2ad8 Doc/library/copy.rst --- a/Doc/library/copy.rst Fri Mar 20 22:05:33 2015 -0700 +++ b/Doc/library/copy.rst Sat Mar 21 06:29:34 2015 +0000 @@ -81,7 +81,10 @@ argument, the memo dictionary. If the :meth:`__deepcopy__` implementation needs to make a deep copy of a component, it should call the :func:`deepcopy` function with the component as first argument and the memo dictionary as second argument. +The :meth:`__deepcopy__` implementation should otherwise consider the memo +dictionary opaque; only this module may add, remove, or modify the keys of the +memo dictionary. .. seealso::