Newbie Q: Class Privacy (or lack of)

[Steve Jobless]

Steve Jobless wrote:
> 
> Hi,
> 
> I just started learning Python. I went through most of the tutorial at
> python.org. But I noticed something weird. I'm not talking about the
> __private hack.
> 
> Let's say the class is defined as:
> 
>   class MyClass:
>     def __init__(self):
>       pass
>     def func(self):
>       return 123
> 
> But from the outside of the class my interpreter let me do:
> 
>   x = MyClass()
>   x.instance_var_not_defined_in_the_class = 456
> 
> or even:
> 
>   x.func = 789
> 
> After "x.func = 789", the function is totally shot.
> 
> Are these bugs or features? If they are features, don't they create
> problems as the project gets larger?
> 
> TIA,
> 
> SJ

Thanks, everyone. I'm hearing that "they are features, but don't use them."

It's not that I'm going to do things like them intentionally.

The first case can be just a typo, like:

  x.valeu = 5

I make typos all the time. Without a spell checker, this message would
be unreadable :).

The second case can be like:

  x.next = y
  y.next = None

to create a linked list by piggybacking "next" to the class. It will
overwrite the iterater for the class if defined.
    If I was working on a large project with many engineers, I'd assume
someone will do things like this sooner or later. I've seen many
horrendous code in my life and I have no control over who I work with.

SJ