[Baypiggies] Trivial OOP pattern problem

[Isaac]

Hi,

Why do you need each of the methods to return the instance?
Can you just wrap the method calls in a function and return the instance?

Cheers,
Isaac


On Fri, Jun 15, 2012 at 12:53 AM, Ian Zimmerman <itz at buug.org> wrote:

>
> I am writing some code using the cairo drawing library, or rather the
> pycairo binding to it.  Unfortunately I sense a bit of API misdesign
> with the binding.  To draw into a context ctx which I obtained somewhat
> like this:
>
> import cairo as C
>
> ctx = C.Context(surface)
>
> I am supposed to write a series of calls like this:
>
> ctx.set_source_rgb(1.0, 1.0, 1.0)
> ctx.rectangle(0.0, 0.0, float(rw), float(rh))
> ctx.fill()
> ctx.scale(sx, sy)
>
> ... and it piles up.  Each of these methods returns None, whilst it
> should conceivably return self, adding a lot of convenience:
>
> ctx.set_source_rgb(1.0, 1.0, 1.0).rectangle(0.0, 0.0, float(rw),
> float(rh)).fill()
>
> I would like to write a wrapper class around Context to enable this
> usage, but I don't know how to do that sanely.  Sure, I could do this:
>
> class ContextWrapper(object):
>
>      def __init__(self, surface):
>          self.ctx = C.Context(surface)
>
>      def fill(self):
>          self.ctx.fill()
>          return self
>
>      def scale(self, sx, sy):
>          self.ctx.scale(sx, sy)
>          return self
>
>          ...
>
> but then I have to wrap each method explicitly, or at least each method
> I use.  I don't consider that sane.
>
> Is there a trick I am missing, perhaps using __dict__ or __getattr__ by
> which I could wrap all the methods wholesale?
>
> --
> Ian Zimmerman
> gpg public key: 1024D/C6FF61AD
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