On 2006-08-25, Paul Rubin <http> wrote: > Bryan Olson <[EMAIL PROTECTED]> writes: >> And herein is the problem: A class may implement "__add__" any >> way the programmer chooses. Python should require, or at least >> document requirements, on further properties of addition. >> Python should insist that addition be symmetric an transitive, >> and classes implementing addition provide an additive >> identity. > > Are you saying "abc"+"def" should not be concatenation? I > guess that's reasonable. As long as + is string concatenation > though, the principle of least astonishment suggests that "sum" > should conconcatenate several strings. > > I'm not sure what you mean by addition being symmetric or > transitive; it is not an equivalence relation. Do you mean > commutative and associative? I'm not sure if floating-point > arithmetic has those properties, strictly speaking.
The interesting part of the discussion, to me, was that Alex Martelli's initial implementation included the string optimization so that a list with a string as its first element called ''.join(lst) instead. But that optimization turns out to be valid only if every element of the list is a string. So there isn't, it seems, a practical way of implementing the sum(list of strings) -> ''.join(list of strings optimization. -- Neil Cerutti 8 new choir robes are currently needed, due to the addition of several new members and to the deterioration of some of the older ones. --Church Bulletin Blooper -- http://mail.python.org/mailman/listinfo/python-list
