Conceptual flaw in pxdom?

[Peter Otten]

Emanuele D'Arrigo wrote:

> This is all good and dandy and it works, mostly. However, if you look
> at the code below for the method __getattr__, it appears to be
> attempting to prevent direct access to -any- variable starting with an
> underscore.
> 
>     def __getattr__(self, key):
>         if key[:1]=='_':
>             raise AttributeError, key
> 
> But access isn't actually prevented because __getattr__ is invoked -
> only- if an attribute is not found by normal means. So, is it just me
> or that little snipped of code either has another purpose or simply
> doesn't do the intended job?

It doesn't do what you think it does; it is there to prevent "infinite" 
recursion. Have a look at the complete method:

>     def __getattr__(self, key):
>         if key[:1]=='_':
>             raise AttributeError, key
>         try:
>             getter= getattr(self, '_get_'+key)
>         except AttributeError:
>             raise AttributeError, key
>         return getter()

If you instantiate the object and try to access the -- non-existent -- 
attribute yadda __getattr__() will be called with key="yadda" which doesn't 
start with an underscore and with gettattr(self, "_get_yadda") triggers 
another __getattr__() call as _get_yadda doesn't exist either. If the check 
weren't there yet another getattr(self, "_get__get_yadda") call would 
follow, and so on until the recursion limit is reached.

Peter