visibility between modules

[Mike Meyer]

"max(01)*" <max2 at fisso.casa> writes:

> hi.
>
> if i have a single program file, different class instances can share
> information in (at least) two fashions:
>
> 1. using instance variables:
>
> class AClass:
>    def __init__(self):
>      self.att_1 = 42
>      self.att_2 = "Hello!"
>
> class AnotherClass:
>    def __init__(self):
>      self.att_1 = anInstanceOfAClass.att_1
>
> anInstanceOfAClass = AClass()
> anInstanceOfAnotherClass = AnotherClass()
> print anInstanceOfAnotherClass.att_1  ### This should print out 42
>
> 2. using globals:
>
> class AClass:
>    def __init__(self):
>      self.att_1 = 42
>      self.att_2 = "Hello!"
>
> class AnotherClass:
>    pass
>
> aGlobalString = "No way."
> anInstanceOfAClass = AClass()
> anInstanceOfAClass.att2 = aGlobalString
> anInstanceOfAnotherClass = AnotherClass()
> anInstanceOfAnotherClass.att_1 = aGlobalString
> print anInstanceOfAClass.att2  ### This should output "No way."
> print anInstanceOfAnotherClass.att_1  ### And this too


Both these methods actually use globals. In ther first case, the
global is "anInstanceOfAClass", that is bound to self.att_1 in the
__init__ method of AnotherClass.

The solution is to pass the instance in as a parameter:

class AClass:
      def __init__(self):
          self.att_1 = 42
          self.att_2 = "Hello!"

class AnotherClass:
      def __init__(self, instance):
          sefl.att_1 = instance

anInstanceOfAClass = AClass()
anInstanceOfAnotherClass = AnotherClass(anInstanceOfAClass)

or maybe just:

anInstaceOfAnotherClass = AnotherClass(AClass())


       <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.