On 9 mar, 11:23, Steven D'Aprano <[EMAIL PROTECTED] cybersource.com.au> wrote: > On Sun, 09 Mar 2008 06:58:15 -0700, Guillermo wrote: > > Okay, so I think I know where's the catch now -- you must rely on the > > fact that the protocol is implemented, there's no way to enforce it if > > you're expecting a parrot-like object. You'd try to call the speak() > > method and deal with the error if there's no such method? > > That's right. That's called "duck typing" -- if all you want is something > that quacks like a duck, then it doesn't matter if it actually is a duck > or not.
In addition to duck typing, in some cases an explicit declaration may be useful: "I implement the Parrot protocol". The zope.interface package does that: there is a way to define interfaces (a set of methods any implementation must provide), and classes can assert "I implement this interface", and one can determine whether a class implements or not certain interface. See http://pypi.python.org/pypi/zope.interface Abstract Base Classes (ABC, for Python 3.0) provide a similar concept (but they're not the same thing). See http://www.python.org/dev/peps/pep-3119/ Of course there is some overlapping between all of these techniques - one should choose the best method in each case. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
