[Python-3000] PEP 3133: Introducing Roles (original) (raw)

Guido van Rossum guido at python.org
Wed May 16 00:39:59 CEST 2007

On 5/15/07, Collin Winter <collinw at gmail.com> wrote:

This is what I don't understand: ABCs require changing the VM, roles don't; all that change buys you is the ability to spell "performs()" as "isinstance()". Why are ABCs preferable, again?

Actually, if you didn't care about overloading isinstance(), you could have everything else in PEP 3119 by using a different spelling than isinstance(). Suppose the playing field were to be leveled like this -- IMO ABCs would still be preferable because they can also be subclassed directly and provide concrete or partially-implemented methods, acting as mix-in classes. You can also turn it around. If Roles were overloading isinstance() -- how would they be better than ABCs?

But I like overloading isinstance(), because it means there's less to learn, and so does Phillip -- it means there can be a uniform way for the GF machinery to talk about the relationships between instances and the various things that can be used as argument annotations (even zope.interfaces could overload isinstance() to do the right thing).

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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