Julien Palard julien at palard.fr
Tue Aug 20 16:04:36 EDT 2019

Hi Vinay,

> I noticed is a list containing single list can identify inner list as a single element of the list whereas in tuples a tuple containing single tuple is unable to identify as a single element unless a comma is specified.

Thanks for reporting!

This is known and documented, quoting the doc [1]:

> A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses). Ugly, but effective. For example:

This is because parenthesis play multiple roles like describing tuples and mathematical priority:


    (1 + 1) * 2

be interpreted "twice the tuple containing the result of 1 + 1" which is (2, 2), or the number 4?

To disambiguate, the trick is to add a trailing coma:

>>> (1 + 1) * 2
>>> (1 + 1, ) * 2
(2, 2)

If you have a better idea, please tell :)

If you worry about it, don't, you won't use often tuples of a single element, and it's still possible to build them, so it's OK.

[1]: https://docs.python.org/3/tutorial/datastructures.html#tuples-and-sequences
Julien Palard

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