Explanation for trailing comma in example from Learning Python?

[Carl Schumann]

Hi,

I am surprised at the trailing comma in the following example from
"Learning Python":

Python 2.3.4 (#1, Dec 10 2007, 15:05:56)
[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

I could see the logic in always or never having a trailing comma. What
I don't understand here is why only the single element case has a
trailing comma. Any explanations please?

Thanks,
Carl Schumann