[Tutor] modified dictionary class

John washakie at gmail.com
Mon Dec 6 16:32:20 CET 2010


Thank you for the response, it's very helpful. I posted a question
earlier to this list (or possibly numpy) about how to create a 'matlab
like structure'. This was early in my learning of Python, and yes, the
intention was to have something that was similar to a matlab
structure... now, I've been using Python much more, and I realize that
this may be in fact 'un-Pythonic'. The problem is, I've used it
extensively throughout my existing modules, and I have become somewhat
comfortable with it...

I guess an alternative would be to simply define a generic class, no?

class Structure(object):

Then, you could easily say:

S = Structure()
S.this = ['my slice of cheese']

and perhaps I would be being more 'pythonic'?? This I could quite
easily do, as, where I have used this class, I almost never actually
use the 'dictionary' like referencing...


On Mon, Dec 6, 2010 at 3:37 PM, Hugo Arts <hugo.yoshi at gmail.com> wrote:
> On Mon, Dec 6, 2010 at 2:47 PM, Alan Gauld <alan.gauld at btinternet.com> wrote:
>> Oops, too quick. I neant to add:
>> But this line seems to return a value so the return values of this function
>> seem to be incompatible which is not a good design pattern.
> I agree it's not the clearest way to do this, but not because of
> incompatible return values. Attribute and Method access have the same
> syntax on objects, and __getattr__ is only called if the attribute
> isn't found "in the usual places," so it won't hide other methods. In
> other words:
>>>> a = Structure()
>>>> a["spam"] = 5
>>>> a.__getstate__()
> None
>>>> a.spam
> 5
> Doesn't look that strange to me, interface-wise. Attribute access
> sometimes returns a function and sometimes not. The comment
> specifically states it's faking a method, so it's pretty clear.
> I do have a few other gripes though:
> * why not just define __getstate__ in the class? why return a new
> lambda every time when you can just write "def __getstate__(self):
> return None"  and be done with it? This also simplifies getattr.
> * it's now impossible to have keys that collide with a method name:
> dict, items, keys, clear, popitem, et cetera. You can set them without
> error, but when you try to get them you'll get the old method, which
> might cause hard-to-find bugs
> * it's not much of an advantage over regular dicts, really. You limit
> yourself to string keys, you make it very unclear that you're using a
> dict, it's not as efficient, and really just unpythonic in general.
> Why do this at all? To make python more Matlab-like?
> Hugo
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