Re: [matplotlib-devel] Use of meta on Artist

[Ryan M. <rm...@gm...>]

On Mon, Nov 26, 2012 at 12:23 PM, Eric Firing <ef...@ha...> wrote:

> On 2012/11/26 7:12 AM, Michael Droettboom wrote:
> > The problem is that I don't think we can do this for all artists.  Some
> > may need to create groupings, or push and pop state even if they are
> > "invisible".  For instance, this is used in the SVG backend to create
> > named groupings (possibly empty) that are referenced from Javascript to
> > provide interactivity.  I think I'd rather keep this to the contained
> > solution in the PR and not try to generalize it beyond that.
> >
> > If we did want to generalize, this would only apply to "leaf node"
> > artists, and not artists that simply exist to contain other artists --
> > and conceivably we could implement that using either a decorator or
> > explicit chaining to a base class, but in any event it would have to be
> > a manual process to determine which artists this would apply to.  We
> > could insert a class in the heirarchy of "ConcreteArtist" (or somesuch)
> > to handle this.
>
> I think we should be rather conservative about this sort of thing.
> Sometimes it is better to just explicitly put the two lines in each
> method than to come up with machinery to do it for you.  Each level of
> depth in an inheritance hierarchy or "meta" chain is an additional level
> of complexity for someone reading the code.  And if someone forgets to
> put in those lines, the penalty is typically from small to nil; but if
> they are put in automatically by fancy methods, and they are not really
> wanted or something else goes wrong, it can make debugging painful.


I think you and Mike are skirting around a key point here. You can always
add the line if you need it, but if you don't need it (or can't use it), by
use of a metaclass, there's no way to "opt out" so to speak.

I'll also add that we don't need to add any more indirection (i.e. another
Python function call) to our drawing stack--we really need to be doing
everything possible to take every last millisecond out of the call to
draw().

Ryan

-- 
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma