[issue19172] selectors: add keys() method

[STINNER Victor]

STINNER Victor added the comment:

If you want to unregister while iterating on .keys(), just copy .keys(), as
I do when removing items from a list or a dict while iterating on it.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue19172>
_______________________________________