Problems with subclassing

[Alexander Stante]

Hello,

I have the following problem. I want to subclass from the pygame class
Surface, but I can't get it working:

class sprite(Surface) :
def __init__(self, image_array, palette):
"some code here"

when I want to create a instance with:

gfx.sprite(arra yi, palette)


I get the following error message:
TypeError: argument 1 must be sequence of length 2, not 100

It seems that the constructor of Surface is not overrided by the one in
sprite, but why?

[Alex Martelli]

Re: Problems with subclassing

Alexander Stante <alex_stante@ya hoo.de> wrote:
[color=blue]
> I have the following problem. I want to subclass from the pygame class
> Surface, but I can't get it working:
>
> class sprite(Surface) :
> def __init__(self, image_array, palette):
> "some code here"
>
> when I want to create a instance with:
>
> gfx.sprite(arra yi, palette)
>
>
> I get the following error message:
> TypeError: argument 1 must be sequence of length 2, not 100
>
> It seems that the constructor of Surface is not overrided by the one in
> sprite, but why?[/color]

It's possible (I'm just guessing) that the problem comes with respect to
__new__ rather than __init__ ...?


Alex

[Gerrit]

Re: Problems with subclassing

Alexander Stante wrote:[color=blue]
> I have the following problem. I want to subclass from the pygame class
> Surface, but I can't get it working:
>
> class sprite(Surface) :
> def __init__(self, image_array, palette):
> "some code here"
>
> when I want to create a instance with:
>
> gfx.sprite(arra yi, palette)
>
>
> I get the following error message:
> TypeError: argument 1 must be sequence of length 2, not 100
>
> It seems that the constructor of Surface is not overrided by the one in
> sprite, but why?[/color]

I think you want to override __new__, not __init__, if if could be
working at all that is. GvR wrote a lengthy introduction to this (among
other things) when Py 2.2 was released: google for "descriptor " and it
should end up somewhere.

It's also possible that Surface is not a viable baseclass at all. You
may want to consult the Pygame mailing list about that.

yours,
Gerrit.

--
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--
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[Chris S.]

Re: Problems with subclassing

Alexander Stante wrote:
[color=blue]
> Hello,
>
> I have the following problem. I want to subclass from the pygame class
> Surface, but I can't get it working:
>
> class sprite(Surface) :
> def __init__(self, image_array, palette):
> "some code here"
>
> when I want to create a instance with:
>
> gfx.sprite(arra yi, palette)
>
>
> I get the following error message:
> TypeError: argument 1 must be sequence of length 2, not 100
>
> It seems that the constructor of Surface is not overrided by the one in
> sprite, but why?
>[/color]

Try manually specifying the subclassed constructor within your new
constructor. For example:

class sprite(Surface) :
def __init__(self, image_array, palette):
Surface.__init_ _(self, someargs)

Then, ensure you are instantiating the subclass correctly.