class scope questions

[Neil Timms]

Not a real star for this sort of thing but...

in the post.. call a is incorrect. a  is a class so we don't call it but 
instaniate it - that is make an object described by a ...thus.. (and we'll 
call it A by convention because it is a class):

(presumes A is already imported)

        myObject = A()


use __init__ and put the variables in there. They are then private (but 
not totally, there is a way...) to instances of the class A. Attributes 
(variables of a class instance ) are best only altered by a setter or 
getter methods = encapsulation.. Now that we have loads of RAM and much 
speed from the CPUs we can use these conventions for more robust and esier 
to read/debug code.

so we can have:

        def setDog(anObject):
                self.dog = anObject

or:

        def getDog():
                return self.dog

or even more cunning (or not) ... the setter getter


        def dog(anObject=''):
                if anObject:
                        self.dog = anObject
                return self.dog

Using the setter/getter version of above - to alter the value of dog we 
would then:


        myObject.dog('puppy')

# the attribute dog of myObject (of class A) now has the value of 'puppy'

to get the value of the attribute dog we would:


        theValueOfDog = myObject.dog()


(sorry just back from finishing a Smalltalk exam - so I'm full of it.).

Basically we hide or variables away from direct access and only alter then 
via methods definind in the class. This restricts the extent of one part 
of the program interacting with others and causing unintended results 
(bugs, or in MS speak features), making implementation and maintenance 
easier - but making us think for the deisgn.

cheers

Neil