Re: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask])
On 2016-04-11 10:45, Ben Finney wrote: > Also, there is another obvious way to create an empty tuple: call > the ‘tuple’ type directly: > > >>> foo = tuple() > >>> print(type(foo), len(foo)) > 0 But here the parens make the tuple too: >>> foo = tuple >>> print(type(foo)) >>> len(foo) Traceback (most recent call last): File "", line 1, in TypeError: object of type 'type' has no len() (totally just yanking chains, throwing pebbles in the pond to watch the ripples, and otherwise sewing confusion ;-) -tkc -- https://mail.python.org/mailman/listinfo/python-list
Re: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask])
On Sun, Apr 10, 2016, at 05:45 PM, Ben Finney wrote: > So, let's please stop saying “parens don't create a tuple”. They do, and > because of that I've stopped saying that false over-simplification. I stand by "parens don't make a tuple", with the caveat that I should have mentioned the empty tuple exception that proves the rule. The only time you need parens is to resolve ambiguity. To suggest that parens do make tuples confuses the issue, given things like this: >>> a = 1,2,3 >>> b = (1, 2, 3) -- Stephen Hansen m e @ i x o k a i . i o -- https://mail.python.org/mailman/listinfo/python-list
Re: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask])
On Mon, Apr 11, 2016 at 10:45 AM, Ben Finney wrote: > So the expanation that remains true when you examine it is: People > wanted a literal syntax to create a zero-length tuple. A pair of parens > is that literal syntax, and it's the parens that create the (empty) > tuple. But parens do NOT create a one-element tuple, and that's usually where people trip up. If you show someone this line of code: x = () and ask what x will be, you might get some wrong responses, but you'll get a lot of people correctly deducing that it's a tuple. The problem is that people see this progression: x = () y = (1) z = (1, 2) and assume they're all tuples. A better progression is this: x = () y = (1,) z = (1, 2,) where every element is followed by a comma and every tuple is surrounded by parentheses. In that situation, everything works. There are slightly different rules about which parts are optional (the parens everywhere except the first case, and the last comma everywhere except the second), but this should be the basic form of tuple progression. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask])
Stephen Hansen writes: > […] parens don't make tuples, commas do. Chris Angelico writes: > The thing you're confused at is that it's not the parentheses that > create a tuple. Parentheses merely group. MRAB writes: > As has been said already, it's the comma that makes the tuple. The > parentheses are often needed to avoid ambiguity. This is too simplistic, and IMO it's just sowing the seed for future confusion. As MRAB states in the same message: > There _is_ one exception though: (). It's the empty tuple (a 0-element > tuple). It doesn't have a comma and the parentheses are mandatory. > There's no other way to write it. So, let's please stop saying “parens don't create a tuple”. They do, and because of that I've stopped saying that false over-simplification. A pair of tuples as an expression is literal syntax to create a tuple with zero items. Also, there is another obvious way to create an empty tuple: call the ‘tuple’ type directly: >>> foo = tuple() >>> print(type(foo), len(foo)) 0 So the expanation that remains true when you examine it is: People wanted a literal syntax to create a zero-length tuple. A pair of parens is that literal syntax, and it's the parens that create the (empty) tuple. -- \ “It is hard to believe that a man is telling the truth when you | `\ know that you would lie if you were in his place.” —Henry L. | _o__) Mencken | Ben Finney -- https://mail.python.org/mailman/listinfo/python-list
