[Python-Dev] Prototypes [was: Proper tail recursion] (original) (raw)

Phillip J. Eby pje at telecommunity.com
Fri Jul 16 18:15:00 CEST 2004

At 09:22 PM 7/15/04 -0400, Raymond Hettinger wrote:

The reason is the feature request is currently out of favor is the possibility that the syntax would be abused and people would start defining their methods outside of class definitions.

That sounds like a feature to me. :) I've just finished drafting an extensible generic function framework using decorators, like this stupid trivial non-motivating example:

 [when("x<2")]
 def fact(x): return 1

 [when("True")]
 def fact(x): return x * fact(x-1)

Generic functions are a great way to structure an extensible framework, where the base function is defined in one module, and then other modules add cases to the function, like:

 from storage_framework import save_ob

 [when("ob in Invoice and db in Oracle")]
 def save_ob(db, ob):
     # code to write Invoice to Oracle

So, with your syntax, you could instead do:

 import storage_framework

 [when("ob in Invoice and db in Oracle")]
 def storage_framework.save_ob(db, ob):
     # code to write Invoice to Oracle

which is much clearer as to intent, although I must confess I have no clue how I'd make it work with my current decorator implemenation, which looks for changes in the frame's locals.

As for declaring methods outside a class, this is actually a good idea for certain generic functions. Say for example that 'save_ob' was actually a method of the database type, rather than being a "free range" generic function. Then, the above would be written as:

 [when("ob in Invoice")]
 def Oracle.save_ob(self, ob):
     # code to write Invoice to Oracle

which is even clearer as to intention.

But, I think that there'd have to be integrated decorator support for it to be really useful, at least for me.

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