On 12/15/05, Chris Mellon <[EMAIL PROTECTED]> wrote: > <snip a bunch of stuff> > > Terminology is important, because we understand the world through > > language. If your language is confused or misleading, your understanding > > will also be confused or incomplete. > > I think the issue is pretty simple, myself: > > With mutable objects, Python has the semantics normally associated > with pass-by-reference. > > With immutable objects, Python has the semantics normally associated > with pass-by-value.
Meant to include this in first post: This is all you have to know to use Python, even very advanced Python. Everything after this point is basically comp-sci trivia and argument about definitions. > > So you could say that Python has both pass-by reference and > pass-by-value (modulo the fact that pass-by-reference doesn't exist at > some level, and is a semantic layer on top of pass-by-value. But > semantics are what we're talking about here). > > However, there is *no way* in Python to get pass-by-value semantics > with a mutable object, or pass-by-reference semantics with an > immutable one (you can build your own scaffolding to mimic it, but the > language won't change it's semantics for you). > > Therefore, it's more correct to say that Python has neither > pass-by-reference semantics or pass-by-value semantics, but some third > thing. And thus the name pass-by-object, where the calling semantics > are that you always get a reference to an object, but what (if any) > other names are bound to that object, or if they can be bound to that > object, depends on the object. > > When you can pass a mutable int to a function (not pass a > namespace/name pair, but a real live mutable int), then Python will > have pass-by-reference. > > When you can pass a list that isn't a shared reference without > explicitly copying it or subclassing it to be immutable, then Python > will have pass-by-value. > > In the meantime, it has pass-by-object. > > > > > > > > > -- > > Steven. > > > > -- > > http://mail.python.org/mailman/listinfo/python-list > > > -- http://mail.python.org/mailman/listinfo/python-list
