On Mon, 04 Jan 2010 06:27:48 -0300, Gabriel Genellina wrote: > En Mon, 04 Jan 2010 05:24:56 -0300, David Williams > <da...@bibliolabs.com> escribió: > >>> py> [1,2,3] + (4,5) >>> Traceback (most recent call last): >>> File "<stdin>", line 1, in <module> >>> TypeError: can only concatenate list (not "tuple") to list >>> >>> In-place addition += does work: >>> >>> py> a = [1,2,3] >>> py> a += (4,5) >>> py> a >>> [1, 2, 3, 4, 5] >> >> I guess to expand a bit more on what I said... What should the result >> be? >> A list or a tuple? The reason += works is because the end result is >> clear; a list. But it is ambiguous in the case of concatenation: did >> you want a tuple or a list? > > Uhm... it seems "obvious" to me that [1,2,3] + (4,5) should be > [1,2,3,4,5]. A list. That's what I would expect, although I cannot > explain why is it *so* obvious to me.
If you can't explain it, it's probably a bad idea. Why should lists be privileged over tuples? How does it work? Do tuples automatically turn into lists, or does the left hand value over-ride the right hand value? In other words, would you expect: "1" + 1 = "11" 1 + "1" = 2 or would you expect: "1" + 1 = "11" 1 + "1" = "11" > Given that 2 + 3.5, and 'abc' + u'def' both return an instance of their > right operand's type, I should probably revise my preconceptions... Yes, you should be a little more careful in your tests. >>> 2 + 3.5 5.5 >>> 3.5 + 2 5.5 Nothing to do with left versus right. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
