On Oct 21, 2013 12:09 PM, "Dhananjay Nene" <dhananjay.n...@gmail.com> wrote: > > On Mon, Oct 21, 2013 at 11:53 AM, Saager Mhatre <saager.mha...@gmail.com> wrote: > > On Oct 21, 2013 11:39 AM, "Dhananjay Nene" <dhananjay.n...@gmail.com> wrote: > >> > >> On Mon, Oct 21, 2013 at 10:55 AM, Saager Mhatre < saager.mha...@gmail.com> > > wrote: > >> > >> > Which generally lead to poor (or at least poorer) abstractions; but I > > digress. > >> > >> Leaky ?? :) > > > > For the most part, yes. > > > >> > > >> >> I think OOPs concepts across a number of languages are quite different. > >> >> You will find python having superior constructs eg. metaclasses etc. > > if you were comparing Python OOP to C++/Java. > >> > > >> > Superior constructs implemented inferiorly. Meteclasses are much^3 more > > powerful in Groovy, Ruby and SmallTalk (where some would claim Python > > borrowed them from; but that's just not true.) > >> > >> I wonder if you meant syntactically/stylistically. Would be keen to > > learn, if there are examples where ruby / groovy (I don't know much about > > smalltalk) allow things that python does not. > > > > Semantically! MetaClasses are a much more powerful construct in those > > languages. > > I'm specifically looking for evidence to support that. And I suspect > it might be out there to be found , just that I haven't so far. One of > my early attempts was documented here > http://blog.dhananjaynene.com/2010/01/dynamically-adding-methods-with-metaprogramming-ruby-and-python/ >
Don't look for metaprogramming, you'll end up with a lot of ancillary stuff. Look for metaclasses or metaobject protocol. > > They form the core of the MetaObjectProtocol which governs the > > dynamic dispatch of messages/methods. Modifications to MetaClasses > > percolate to Classes and objects they are associated with and such > > modifications as well as MetaClass associations can be dynamic as well as > > temporary; leading to some seriously powerful use cases. > > The "temporary" is intriguing. I don't quite yet understand what it > means .. does it mean you could say temporarily add a method and then > take it out later (or some other similar capability) ? Yup! Look for Categories. The Groovy guides have a bunch of examples. (Nothing to do with category theory AFAIK) > > > > That's pretty much what always foiled my attempts at understanding Python > > MetaClasses, I was looking for power where there was none to find. The best > > comparison I could find was to Groovy's Compile time AST transforms, but > > even those are even more powerful as they drop down a level of abstraction > > and hand you the AST for the an rated element. > > AST transforms are sort of feasible but rarely done, and not sure if I > would like to be a part of such an exercise. They kick in via the > import hook, thus you build the AST on your own, thankfully python > does provide AST helpers. Googling for python macros will show some > such valiant attempts - https://github.com/lihaoyi/macropy or > https://code.google.com/p/metapython/wiki/Tutorial While I haven't implemented any yet, Groovy's AST transforms make implementation as well as application fairly easy. But, that wasn't my point. What I meant was that Python's meta classes only kick in at module/lass load time whereas Metaclasses in the other languages play a greater role at runtime. - d _______________________________________________ BangPypers mailing list BangPypers@python.org https://mail.python.org/mailman/listinfo/bangpypers
