On 23/05/2018 14:11, Steven D'Aprano wrote:
On Wed, 23 May 2018 11:10:33 +0100, bartc wrote:
(x,) Tuple of one item
Incorrect. Yet again, you have failed to do enough testing. No special
form is required. Only a comma:
py> x = 1,
py> type(x)
<class 'tuple'>
It isn't enough to test examples which confirm a hypothesis. You need to
test examples which also refute it, and see if your hypothesis survives
the challenge.
I use this trailing comma scheme in my own own languages too. The reason
is simple, it is to distinguish between these two:
(x) Ordinary bracketed expression
(x) A list (in my case) of one item.
That is not needed for one less item: (), or one more: (x,y). Like
Python, that trailing comma is not needed for [x] (I don't have a {...}
constructor).
In both languages, it's just a hack to get around a syntax clash in the
language.
I don't say however, that the comma is the defining feature of a list.
Comma is used to separate items of /any/ kind of list, and that trailing
comma is used when there is an ambiguity or a conflict.
--
bartc
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