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"Data blocks" syntax specification draft

On 22/05/2018 15:25, Chris Angelico wrote:
> On Tue, May 22, 2018 at 8:25 PM, bartc <bc at freeuk.com> wrote:
>> Note that Python tuples don't always need a start symbol:
>>     a = 10,20,30
>> assigns a tuple to a.
> The tuple has nothing to do with the parentheses, except for the
> special case of the empty tuple. It's the comma.

No? Take these:

  a = (10,20,30)
  a = [10,20,30]
  a = {10,20,30}

If you print type(a) after each, only one of them is a tuple - the one 
with the round brackets.

The 10,20,30 in those other contexts doesn't create a tuple, nor does it 


Or here:

   def g(a,b,c):

Or here in Python 2:

   print 10,20,30

and no doubt in a few other cases. It's just that special case I 
highlighted where an unbracketed sequence of expressions yields a tuple.

The comma is just generally used to separate expressions, it's not 
specific to tuples.