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From: Ian Kelly <ian.g.kelly@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Dynamic object attribute creation
Date: Mon, 29 Feb 2016 09:33:48 -0700
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On Mon, Feb 29, 2016 at 9:06 AM, Random832 <random832@fastmail.com> wrote:
> On Mon, Feb 29, 2016, at 10:36, ast wrote:
>> but why doesn't it work with built-in classes int, float, list.... ?
>>
>> L = [1, 8, 0]
>> L.test = 'its a list !'
>>
>> (however lists are mutable, int, float ... are not)
>
> Because those classes do not have attribute dictionaries, in order to
> save space.
>
> You can make a class without an attribute dictionary, by using
> __slots__.

You can also make a list that does have an attribute dictionary by
subclassing it.

>>> class MyList(list): pass
...
>>> obj = MyList()
>>> obj.test = 'foo'