Earlier quoted context omitted.
if var: ... is better code (for my value of better, which is subjective) than: if var is not None: ...
In my opinion, the "explicit is better than implicit" mantra of Python (which I find very sensible) should immediately imply preference for the second, even in cases where the first is almost certainly not going to cause problems. Testing for "not None" also immediately tells other devs at least something about what's going on. Example: If var is an argument to a function and you see "if var," really understanding wh…
self foo isNil ifTrue: [self defaultFoo]
later some implementations added a method on object to test for nil
self foo ifNil: [self defaultFoo]
if you had to test for nil before testing for a condition it would be a bit ugly.
self foo ifNil: [((self foo) isFooish) ifTrue: [self defaultFoo]]
In ruby which was developed about a bit later perhaps to late to influence pythons bool handling they got rid of this problem by treating either nil or false as Falsey and everything else as truthy.
In python everything is true except:
None
False
zero of any numeric type, for example, 0, 0L, 0.0, 0j.
any empty sequence, for example, '', (), [].
any empty mapping, for example, {}.
instances of user-defined classes, if the class defines a __nonzero__() or __len__() method, when that method returns the integer zero or bool value False. [1]
The upside to python behaving like this is that in many situations you don't care what kind of falsey value you may have and you can write
if person and person.name: instead of if person != None and person.name != None and person.name != "":
and
if students and "John" in students and students[John"].age and students[John"].friends: print "John has friends" instead of if students != None and "John" in students and students[John"].age != None and len(students[John"].friends) > 0: print "John has friends"
There are downsides to this and people may have a strong personal preference for personal scripts and you can argue that the ruby way or even the smalltalk way is conceptually nicer(and more "explicit") but this is proper pythonic style and generally you should use it in python(maybe not the numerical one except when getting len of a collection)(unless you specifically depend on different code for different falsey values).