[docs] Bug report

[Georg Brandl]

On 05/04/2016 01:51 AM, Christian Yeganeh wrote:
> I have found a bug. Its small and not harmful. But its still there. If you take the string of a tuple, it will not always return the correct string. 
> If you have a tuple with only one element and cast it using str() it will put the comma at the end of the string before the ) as if there was a second element. 
> 
> sample code:
>>>> class testclass:
> ...     def __repr__(s): return 'a'
> ... 
>>>> (1,2)[1:]
> (2,)
>>>> tuple([1])
> (1,)
...

Hi Christian,

this is not a bug, but expected behavior: since 1-tuples are a valid type,
we have to distinguish them from simply parenthesized expressions by the
trailing comma.  You can see that when trying to write a 1-tuple literal:

>>> (1)
1
>>> (1,)
(1,)

And the repr output just mirrors the input syntax.

cheers,
Georg

BTW, trailing commas are also allowed whenever you have a comma-separated
list in Python.  Always using a trailing comma for line-by-line lists
helps in reducing diff churn and not forgetting the comma when adding
elements.

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