[Tutor] attributes vs globals (was Re: global list)

[Albert-Jan Roskam]

________________________________
> From: Alan Gauld <alan.gauld at btinternet.com>
>To: tutor at python.org 
>Sent: Friday, April 25, 2014 12:15 AM
>Subject: Re: [Tutor] attributes vs globals (was Re: global list)
> 
>
>On 24/04/14 21:48, Mark Lawrence wrote:
>> On 24/04/2014 21:30, Albert-Jan Roskam wrote:
>>>
>>> As a side not, I find that variables (attributes) defined in __init__
>>> are also much like globals, but that's probably a different discussion.
>>
>> Would you please be kind enough to explain your logic.
>
>I can't speak for Albert but I do tend to agree that class
>(or instance) variables are a lot like globals. They are
>slightly better controlled because they are unique to an
>instance but they do result in code(methods) that are
>dependant on side effects. You are changing data that
>is neither passed into the method or returned by it.
>So its not obvious which instance attributes are being
>modified by which methods.
>
>Now OOP theory says that with information hiding you
>shouldn't care, so long as the external behaviour is
>the correct, but in Python its  common to directly
>access attributes. And if you inherit a class you
>often do care about its internal state.
>
>So instance variables carry many of the same negative
>characteristics that globals do, albeit confined to a
>single entity and a single, constrained, set of functions..


Hi all,

Sorry for the delayed reply, I was on holiday. Yes, Alan said what I meant with my original (somewhat vague) description.
The snippet below further illustrates this (orignally I had only pseudo_global2 in mind, but the pseudo_global1 is another option). self.pseudo_global*'s value can be accessed everywhere, even though it is not an argument of the function or method.


class Foo(object):
    pseudo_global1 =  "I am all over the place, if I want to"
    def __init__(self):
        self.pseudo_global2 = "I am also all over the place, if I want to"
        print self.pseudo_global2
    def some_method(self):
        print self.pseudo_global2
        def some_function():
            print self.pseudo_global2
        some_function()
        print Foo.pseudo_global11

if __name__ == "__main__":
    Foo().some_method()


regards,
Albert-Jan