On Sun, 3 Jun 2012 23:43:30 +0200
Tehn Yit Chin <tehn.yit.c...@gmail.com> <tehn.yit.c...@gmail.com> wrote:
> Hi all,
>
> I am trying to understand when it is appropriate to use None as in the
> following example
>
> if abc != None:
> print "abc is not None"
>
The proper idiom, for a variety of reasons, is:
if abc is not None:
# do stuff
> 1) Can I use it to determine if the variable abc exists?
>
No. It will raise a NameError, which you would have to catch. To do
what you want, something along the lines of:
try:
abc
# it exists
except NameError:
# it doesn't
However, this is pretty dirty. Why are you using variables that
potentially don't exist?
> 2) Can I use it to determine if the variable abc does not contain
> anything?
>
For a generic foo,
if foo not in abc:
# it's not there, Jim
Does this answer your questions?
(I've been away from Python for a bit, one of the other tutors might
correct me with better practice things, I'm rusty!)
--
Corey Richardson
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
