Strange result ffor object to bool

[Chris Angelico]

On Fri, Nov 25, 2011 at 5:52 PM, ZhouPeng <zpengxen at gmail.com> wrote:
> I am sure listen is not None and can be accessed properly.
>
> But print bool(listen) is False
> if not listen  is True

Casting something to boolean follows strict rules derived from the
notion that emptiness is false and nonemptiness is true. For instance:

>>> bool(""),bool([]),bool({}),bool(0)
(False, False, False, False)

Details here: http://docs.python.org/library/stdtypes.html

Chris Angelico