*Spoiler:* You've convinced me. On 7 November 2012 14:00, Oscar Benjamin <oscar.j.benja...@gmail.com> wrote:
> On 7 November 2012 13:39, Joshua Landau <joshua.landau...@gmail.com> > wrote: > > On 7 November 2012 11:11, Oscar Benjamin <oscar.j.benja...@gmail.com> > wrote: > >> A more modest addition for the limited case described in this thread > could > >> be to use exponentiation: > >> > >> >>> [0] ** (2, 3) > >> [[0, 0, 0], [0, 0, 0]] > > > > Hold on: why not just use multiplication? > > > >>>> [0] * (2, 3) > > > > is an error now, and it makes total sense. Additionally, it's not > breaking > > the "no copy -- _ever_" rule because none of the lists existed before. > The > > values inside the list would be by reference, as before, so lst * (x,) > would > > be the same as lst * x if x is an integer. > > The problem is that this operation is asymmetric. Currently int/list > multiplication is commutative so that: > > ['a', 'b'] * 2 == 2 * ['a', 'b'] > I see. I agree that that is a valid point. Remember, though, that we could just keep this behaviour: [0] * (2, 3) == (2, 3) * [0] > If you use this kind of multiplication what happens to the other > cases? e.g. what do you give for: > > >>> [0] * [2, 3] > Nothing. If you allowed lists to multiply this time, why not with your suggestion? We should require a tuple and a list. > >>> [2, 3] * [0] > Same. > >>> (2, 3) * [0] > == [0] * (2, 3) > >>> (2, 3) * (4, 5) > Nothing. > and so on. Although Python does not guarantee commutativity of > multiplication in general I think that since for lists it has always > been commutative it would be bad to change that. > Agreed > Exponentiation is expected to be asymmetric and is currently unused so > there is no ambiguity. The problem is if someone has already > subclassed list and added an exponentiation method. How is that a problem? They just wont get the functionality. That said, losing: [0] * (2, 3) == [0] * [2, 3] would mean losing duck-typing in general. *Thus*, I fully agree with your choice of exponentiation.
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