Jim Jewett <jimjjewett@gmail.com> wrote:

(In http://mail.python.org/pipermail/python-dev/2005-October/057409.html,) Nick Coghlan suggested allowing attribute references as binding targets.

...

x = property("Property x (must be less than 5)")

...

def x.get(instance): ...

Josiah shivered and said it was hard to tell what was even intended, and (in http://mail.python.org/pipermail/python-dev/2005-October/057437.html) Nick agreed that it was worse than

...

x.get = f given: def f(): ...

Could someone explain to me why it is worse?

def x.get(...): ... Seems to imply that one is defining a method on x. This is not the case. It is also confused by the x.get(instance) terminology that I doubt has ever seen light of day in production code. Instance of what? Instance of x? The class? ... I'm personally averse to the 'given:' syntax, if only because under certain situations, it can be reasonably emulated.

I understand not wanting to modify object x outside of its definition.

I understand that there is some trickiness about instancemethods and bound variables.

But these objections seem equally strong for both forms, as well as for the current "equivalent" of

def f(): ... x.get = f

The first form (def x.get) at least avoids repeating (or even creating) the temporary function name.

The justification for decorators was to solve this very problem within a module or class. How is this different? Is it just that attributes shouldn't be functions, and this might encourage the practice?

Many will agree that there is a problem with how properties are defined. There are many proposed solutions, some of which use decorators, custom subclasses, metaclasses, etc. I have a problem with it because from the description, you could use... def x.y.z.a.b.c.foobarbaz(...): ... ...and it woud be unclear to the reader or writer what the hell x.y.z.a.b.c is (class, instance, module), which can come up if the definition/import of x is far enough away from the definition of x.<blah> . Again, ick. - Josiah