'if name is not None:' v. 'if name:'

Reedick, Andrew jr9445 at ATT.COM
Tue Jul 15 22:13:18 CEST 2008



> -----Original Message-----
> From: python-list-bounces+jr9445=att.com at python.org [mailto:python-
> list-bounces+jr9445=att.com at python.org] On Behalf Of Victor Noagbodji
> Sent: Tuesday, July 15, 2008 3:44 PM
> To: python-list at python.org
> Subject: Re: 'if name is not None:' v. 'if name:'
> 
> >>what's the difference between these two statement?
> >one checks if the given object is not None, the other checks if it's
a
> true value:
> >http://docs.python.org/ref/Booleans.html#Booleans
> >>And which one should one use?
> >depends on what you want to test for, of course.
> >
> ></F>
> 
> Well that's exactly why I'm asking. Since None returns False in if
> statements. Why do people use if name is not None: instead of simply
> writing if not name?
> 


If name is None:
    Then name is NULL, nothing, nada, no object, no memory allocated, a
NULL pointer

If name is not None:
    Then name is an object.  It's a pointer to some kind of allocated
structure in memory.  No idea if it contains a false or true value.

If name:
    Then either
        a) name is an object, and that object does not have a 'false'
value, such as False, zero, or empty.
          or
        b) name is NULL/None.  No object.


Try this:

d = dict()
if not d:
	d['a'] = 1
print d

d = None
if not d:
	d['c'] = 3
print d





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