[Tutor] Re: Newbie OOP Question.(diff between function, module and class)

[Alexandre Ratti]

At 16:36 10/06/2002 -0500, SA wrote:
> > globalFoo = "I am a global variable."
> >
> > class Test:
> >    classFoo = "I am a class variable."
> >
> >    def __init__(self):
> >        self.instanceFoo = "I am an instance variable."
> >        localFoo = "I am a local variable."
> >        print globalFoo
> >        print self.classFoo
> >        print self.instanceFoo
> >        print localFoo
> >
> > if __name__ == "__main__":
> >    t = Test()

>1. How does "print self.classFoo" know to print classFoo if the classFoo
>    variable is defined prior to the __init__(self) function?

Here, classFoo is a class attribute, whereas instanceFoo is an instance 
attribute. A class attribute is defined when the class is defined; it is 
available in all class instances (they share a common copy of the class 
attribute).

>2. What is the purpose of the line "if __name__ == "__main__":"? (How does 
>it work and why do you use this instead of just running "t = Test"?)

This is often used in Python for testing code. This condition is only true 
when the module is executed as standalone code; it is not true when the 
module is imported into another module. So you can store testing code after 
this condition; it won't run when the module is imported.

If you just use "t = Test" as top-level code in the module, it will be 
executed everytime (even when the code is imported into another module), 
which may not be what you want.


Cheers.

Alexandre