CODEWITHSUNDEEP
pythonset
my_question
my_question

Reputation: 3235

Python tuple() : when does it reorder?

I am using Python 3.7 and get confused at tuple(). Sometimes it re-order the data, sometimes not:

>>> a=tuple([2, 1, 3])
>>> print(a)
(2, 1, 3)   <== the tuple from list is not re-ordered

>>> s={2, 1, 3}
>>> b=tuple(s)
>>> print(b)
(1, 2, 3)   <== the tuple from set is re-ordered

>>> print(tuple({10, 5, 30}))
(10, 5, 30)  <== the tuple from set is not re-ordered

>>> print(s)
{1, 2, 3}    <== the set itself is re-ordered

I have 2 questions:

  1. What are expected behavior of tuple() as of whether:

    1.1 Generate an ordered tuple?

    1.2 Modify the input?

  2. Where can I find the definitive documentation? I checked Python on-line doc, https://docs.python.org/3/library/stdtypes.html#tuple, it does not provide such info at all.

Thanks.

Upvotes: 1

Views: 385

Answers (3)

Axblert
Axblert

Reputation: 576

Tuples are by definition an ordered data structure and their constructor is tuple() .

In your case, if you're using {}, its not a tuple but a set and therefore not ordered.

You can find the official python tutorial here. In 5.3 they also address tuples specifically

Upvotes: 1

buran
buran

Reputation: 14233

As stated in the link you shared:

The constructor builds a tuple whose items are the same and in the same order as iterable’s items.

Because set is un-ordered by definition, if you pass set as iterable to tuple() function there is no way to know/guarantee the order.

Upvotes: 3

Bennett Brown
Bennett Brown

Reputation: 5373

A set is unordered, and a list is ordered. So tuple(a_list) retains the order of the list but tuple(a_set) has no stated order to follow.

Upvotes: 5

Related Questions