The meaning of "="

[Piet van Oostrum]

>>>>> aahz at pythoncraft.com (Aahz) (A) wrote:

>A> In article <m27hybyo95.fsf at cs.uu.nl>, Piet van Oostrum  <piet at cs.uu.nl> wrote:
>>>>>>>> aahz at pythoncraft.com (Aahz) (A) wrote:
>>> 
>A> In article <m24otg3hkk.fsf at cs.uu.nl>, Piet van Oostrum
>A> <piet at cs.uu.nl> wrote: 
>>> 
>>>>>> And to get c.x = 4 working you also need a __setitem__. 
>>> 
>A> Nope.  You do need __setitem__ so that this works:
>>> 
>A> c['x'] = 4
>>> 
>>> Sorry, I meant such that c.x = 4 does the same as c['x'] = 4 because
>>> that was what the OP wanted (I think).

>A> c.x = 4 
>A> already updates the instance dict, so there's no need to change any class
>A> methods to support it.  That is, IME it's much better to add methods to
>A> a regular class to make it more dict-like using the built-in instance
>A> dict rather than changing any of the attribute mechanisms.  If you're
>A> really curious, I recommend trying several approaches yourself to see
>A> what works better.  ;-)

Yes, that's why I mentioned __setitem__. I just mixed up the motivation.

In [28]: class AttrDict:
   ....:     def __getitem__(self, key):
   ....:         return getattr(self, key)
   ....:     
   ....:     def __setitem__(self, key, value):
   ....:         setattr(self, key, value)
   ....:         
   ....:         

In [29]: c = AttrDict()

In [30]: c["y"] = 3

In [31]: c.y
Out[31]: 3

In [32]: c.x = 4

In [33]: c['x']
Out[33]: 4

-- 
Piet van Oostrum <piet at cs.uu.nl>
URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: piet at vanoostrum.org