[issue28128] Improve the warning message for invalid escape sequences

[Ned Deily]

Ned Deily added the comment:

It sounds like a fix but let's see the final patch first.  If a core developer wants to apply it to the default branch for 3.7, we can decide whether it should go into 3.6, too.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28128>
_______________________________________