[Types-sig] tuples (was: New syntax?)

[Guido van Rossum]

> On Sat, 18 Dec 1999, Paul Prescod wrote:
> > Greg Stein wrote:
> > > 
> > > Bite me. :-)
> > > 
> > > You do raise a good point in another post, however:
> > > 
> > >   def foo(*args: (Int)):
> > 
> > Python should not use tuples as "read-only lists." From a type-system
> > point of view, a tuple should be a fixed-length, fixed-type data
> > structure defined at compile time.

[Greg again]
> Ideal or not, this is the current situation. *args is a tuple.
> 
> Are you suggesting a particular change here? If so, then add it to your
> issues list :-)  [you are maintaining one, right? :-)]

I don't think there's a good, deep reason why *args yields a tuple;
only a historical one.

I think that originally, all argument lists were internally passed
around as tuples, because (in *very* early Python) argument lists
*were* tuples.

There's no particular reason why it should be immutable -- after all
**kwargs returns a dict, which is mutable.

The only reason not to switch to tuples is backwards compatibility --
in particular there is a lot of code (e.g. in the std library) that
creates new arg lists by adding tuples to *args.  This could be solved
by allowing + to operate on a mix of lists and tuples.  I think the
result should yield a list.

Not a strong argument to do this, just a relaxation of Greg's argument
that *args is a tuple -- it needn't be, if we have a good reason to
change it.

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