OOP techniques in Python

[Philippe Martin]

Edward Elliott wrote:

> Panos Laganakos wrote:
>> i.e. we usually define private properties and provide public functions
>> to access them, in the form of:
>> get { ... } set { ... }
>> 
>> Should we do the same in Python:
>> Or there's no point in doing so?
>> 
>> Some other techniques come to mind, but I think that Python tends to
>> allow the programmer to access stuff he wants even though he shouldn't
>> or in the form of a dict or list, rather than a method to do so.
> 
> There's no point.  Private access can only be advisory anyway -- there are
> ways around it in every language.  Convention serves just as well, people
> know that touching _foo is done at their own risk.  It's not creating
> extra hoops to jump through the few times you really do need to touch a
> private var.
> 
> Others already mentioned how to transparently change attributes to
> properties.
> 
> If you're worried about enforcing restrictions in your code base, get a
> lint checker to flag any expression of the form name._foo where name isn't
> 'self'.  Yes you can still access _foo other ways, but you'll never get
> perfect enforcement anyway.  Maybe the extra step will make you think
> twice, if that's what you want (and it seems to be).

-- 

What then is the point of the double underscore (if any) ?:


In [2]:class test:
   .2.: _one_underscore=1
   .2.: __two_underscores=2
   .2.:

In [3]:t = test()

In [4]:t._one_underscore=2

In [5]:t.__two_underscores=3

In [6]:t.__two_underscores
Out[6]:3

In [7]:dir (test)
Out[7]:['__doc__', '__module__', '_one_underscore',
'_test__two_underscores']

In [8]:test._one_underscore
Out[8]:1

In [9]:test.__two_underscores
---------------------------------------------------------------------------
exceptions.AttributeError                            Traceback (most recent
call last)

/home/philippe/<ipython console>

AttributeError: class test has no attribute '__two_underscores'



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"Poignée trop essorée, moulin bien rincé"
Pierre Lafouine
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