OOP techniques in Python

[Steven Bethard]

Dennis Lee Bieber wrote:
> On Thu, 27 Apr 2006 14:32:15 -0500, Philippe Martin
> <pmartin at snakecard.com> declaimed the following in comp.lang.python:
> 
>> What then is the point of the double underscore (if any) ?:
> 
> 	To prevent masking/shadowing of inherited attributes...

Note that it can fail to do this if you accidentally (or purposefully) 
name a class the same as a parent or ancestor class:

 >>> class Confusion(object):
...     def __init__(self):
...         self.__str = 'module 1'
...     def get_module_1_confusion(self):
...         return self.__str
...
 >>> module_1_confusion = Confusion
 >>> class Confusion(module_1_confusion):
...     def __init__(self):
...         self.__str = 'module 2'
...
 >>> module_2_confusion = Confusion
 >>> module_2_confusion().get_module_1_confusion()
'module 2'

So you still need to at least check that the name of your subclass is 
different from the name of all its ancestors.  This doesn't come up that 
often, but I know a few people have been bitten by it.

STeVe