Anders J. Munch wrote:
Ethan Furman wrote:
> Even if we find out that C.__nonzero__ is called, what was it that
> __nonzero__ did again?
reinforce the impression that he is unaware of the double-underscore
functions and what they do and how they work.
Only if your newsreader malfunctioned and refused to let you read the
rest of the paragraph.
Of course I know what __nonzero__ does.
regards, Anders
Anders, my apologies. Since reading that post I came across some other
replies you made and realized quite cleary that you do know what you're
doing.
By way of explanation as to why I was confused: the "even if we find
out" suggested to me that you weren't aware of the calling pattern for
"if x" (__nonzero__ if defined, otherwise __len__ if defined). Also, in
your sample code you defined a class C, then assigned the variable c
using "c=get_a_C()", and get_a_C was never defined. Then you posed the
question, "if get_a_C might ever return None"... who knows? You never
said what get_a_C did; furthermore, whether or not get_a_C returns a C
object or None is completely irrelevant to whether or not __nonzero__ is
defined or attribute_is_nonnegative is defined.
FWIW, I completely agree with you as far as naming functions that deal
with less consequential attributes; for an attribute that is central to
the object, I agree with using __nonzero__. For example:
--------------------------------------------------------------------
class Human(object):
def __init__(self, hair, eye, skin):
self.alive = True
self.haircolor = hair
self.eyecolor = eye
self.skincolor = skin
def __nonzero__(self):
return self.alive
def hair_color_is_red(self):
return self.haircolor in ['red', 'strawberry blonde', 'auburn']
def eye_color_is_green(self):
return self.eyecolor in ['green', 'hazel', 'teal']
def skin_color_is_medium(self):
return self.skincolor in ['tanned', 'brown', 'burnished']
def die(self):
self.alive = False
def talk(self):
if self:
print "I don't want to go in the cart!"
def walk(self, where=''):
if self:
if not where:
print "Just taking a stroll..."
else:
print "On my way to " + where
--> from human import Human
--> charles = Human('blonde', 'teal', 'sunburnt')
--> charles
--> charles = Human('blonde', 'teal', 'sunburnt')
--> if charles:
... charles.eye_color_is_green()
... charles.walk("away from the cart...")
... charles.talk()
...
True
On my way to away from the cart...
I don't want to go in the cart!
--------------------------------------------------------------------
If charles is alive is rather important to the whole object -- if he's
dead, he's not walkin' and talkin'! ;)
~Ethan~
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