[Python-Dev] Re: "groupby" iterator

[David Eppstein]

In article 
<200312031748.hB3Hm5504233 at c-24-5-183-134.client.comcast.net>,
 Guido van Rossum <guido at python.org> wrote:

> > A minor correction: the Voodoo approach handles fine method calls by
> > defining a __call__ method in the Voodoo class; [...]
> > 
> > lambda x: x.startswith("text")
> > This works fine as:
> > Voodoo().startswith("text")
> 
> Hm.  But the whole point of Voodoo is that the resulting object has a
> __call__ method that evaluates the expression for a given argument.
> How do you do that?  (I suppose you can do it if you don't do
> chaining, but I like the chaining.)

I think you would need two kinds of voodoo.
    extract.attr
could expand to
    lambda x: x.attr
(or something similar via __call__ methods) but
    method.startswith
could expand to
    lambda *args: lambda x: x.startswith(*args)

Then you could do
    sort(stringlist, key=method.count("kibo"))
or whatever.

Obviously this doesn't allow you to easily express e.g. methods of 
attributes, but beyond a certain level of complexity you should be using 
separate defs anyway.

-- 
David Eppstein                      http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science