Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Ben Finney <ben+python@benfinney.id.au>
Newsgroups: comp.lang.python
Subject: Parens do create a tuple (was: one-element tuples [Was: Most probably a stupid question, but I still want to ask])
Date: Mon, 11 Apr 2016 10:45:08 +1000
Lines: 49
Message-ID: <mailman.0.1460335519.15650.python-list@python.org>
References: <neelcl$mer$1@gioia.aioe.org> <neeq6v$ruk$1@gioia.aioe.org> <1460333911.3449208.574628345.4B46CD32@webmail.messagingengine.com> <85r3ed2ctn.fsf_-_@benfinney.id.au>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Cancel-Lock: sha1:MBVnM/y5qjkE6hkQ9Mdy9ZlhIL4=
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux)
Precedence: list
Xref: csiph.com comp.lang.python:106815

Stephen Hansen <me+python@ixokai.io> writes:

> […] parens don't make tuples, commas do.


Chris Angelico <rosuav@gmail.com> writes:

> The thing you're confused at is that it's not the parentheses that
> create a tuple. Parentheses merely group.


MRAB <python@mrabarnett.plus.com> 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))
    <class 'tuple'> 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