ways to declare empty set variable

[Ben Finney]

bearophileHUGS at lycos.com writes:

> In Python ( ) denote:
> - expression grouping
> - they are very often used to denote tuples (despite being necessary
> only for the empty one)
> - generators (x for x in ...).
> The Boo language shows that () aren't that necessary for the
> generators.

Now, that one I *am* sure of. Generator literals do not require the
parens at all. However, the syntax of where the generator literal
*appears* can make it necessary to explicitly group the expression
using parens.

    >>> import string
    >>> list(char for char in string.digits)
    ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
    >>> char for char in string.digits
      File "<stdin>", line 1
        char for char in string.digits
               ^
    SyntaxError: invalid syntax

So, it's not that parens are "used for generator literals". It's that
parens can be used to make grouping explicit where the syntax would
otherwise be ambiguous.

-- 
 \     "If you're a horse, and someone gets on you, and falls off, and |
  `\      then gets right back on you, I think you should buck him off |
_o__)                                     right away."  -- Jack Handey |
Ben Finney