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Question about implementing immutability


On 2018-11-21 17:45, Iwo Herka wrote:
> Hello,
> 
> Let's say I want to implement immutability for user-defined class.
> More precisely, a class that can be modified only in its (or its
> super-class') __init__ method. My initial idea was to do it the
> following fashion:
> 
>     def __setattr__(self, *args, **kwargs):
>         if sys._getframe(1).f_code.co_name == '__init__':
>             return super().__setattr__(*args, **kwargs)

I don't like this. First of all, it's needlessly cryptic, and secondly
this allows other classes' __init__s to set attributes.

I might try setting a self._fixed flag at the end of init and do a check

if getattr(self, '_fixed', False):
    raise TypeError(f"'{type(self)}' is immutable")

but this presumably comes with other problems.

>         raise AttributeError()

This should be TypeError.