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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Bitten by my C/Java experience
Date: Mon, 04 May 2015 16:06:29 -0400
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Xref: csiph.com comp.lang.python:89929

On 5/4/2015 1:43 PM, Ian Kelly wrote:

> *    () is a zero-element tuple, and (a, b) is a two-element tuple,
> but (a) is not a one-element tuple. Tuples are created by commas, not
> parentheses, so use (a,) instead.

Which means that a, and a,b (or a,b,) are 1 and 2 element tuples 
respectively. Except for empty tuples, parentheses are optional unless 
needed to fence off the tuple from surrounding code (which happens to be 
most of the time, but not always).  A trailing comma is prohibited for 
zero element tuples, required for one element tuples, and optional for 
multiple element tuples.

-- 
Terry Jan Reedy