How can I make an instance of a class act like a dictionary?

Chris Rebert clp2 at rebertia.com
Mon Feb 27 08:39:01 CET 2012


On Sun, Feb 26, 2012 at 11:24 PM, John Salerno <johnjsal at gmail.com> wrote:
> Hi everyone. I created a custom class and had it inherit from the
> "dict" class, and then I have an __init__ method like this:
>
> def __init__(self):
>        self = create()
>
> The create function creates and returns a dictionary object. Needless
> to say, this is not working. When I create an instance of the above
> class, it is simply an empty dictionary rather than the populated
> dictionary being created by the create function. Am I doing the
> inheritance wrong, or am I getting the above syntax wrong by assigning
> the return value to self?

Assignment to `self` has no effect outside the method in question;
Python uses call-by-object (http://effbot.org/zone/call-by-object.htm
) for argument passing.
Even in something like C++, I believe assignment to `this` doesn't work.

> I know I could do self.variable = create() and that works fine, but I
> thought it would be better (and cleaner) simply to use the instance
> itself as the dictionary, rather than have to go through an instance
> variable.

Call the superclass (i.e. dict's) initializer (which you ought to be
doing anyway):
    super(YourClass, self).__init__(create())

Cheers,
Chris
--
http://rebertia.com



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