[Tutor] Python Generator expressions

[Steven D'Aprano]

On Wed, Jul 24, 2019 at 11:26:26AM +1200, David L Neil wrote:

> Clarifying the difference/similarity in appearance between a generator 
> expression and a tuple, it might help to think that it is the comma(s) 
> which make it a tuple!

David makes an excellent point here. Except for the special case of the 
empty tuple, it is *commas* that create tuples, not parentheses. The 
round brackets are used for grouping, and are optional:

py> a = 1, 2, 3
py> type(a)
<class 'tuple'>


The only times you *need* parens around a non-empty tuple is to group 
the items or to avoid ambiguity, e.g. a tuple inside a tuple:

a = 1, 2, (3, 4, 5), 6
assert len(a) == 4

or when passing a literal tuple as argument to a function:

function(1, 2, 3, 4, 5, 6)    # six arguments
function(1, 2, (3, 4, 5), 6)  # four arguments




-- 
Steven