How to get a list from a set?

Question

How do I get the contents of a set() in list[] form in Python?

I need to do this because I need to save the collection in Google App Engine and Entity property types can be lists, but not sets. I know I can just iterate over the whole thing, but it seems like there should be a short-cut, or "best practice" way to do this.

Asked By: Chris Dutrow

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Source

Answer 1

>>> s = set([1, 2, 3])
>>> list(s)
[1, 2, 3]

Note that the list you get doesn’t have a defined order.

Answered By: Sven Marnach

Answer 2

See Sven’s answer, but I would use the sorted() function instead: that way you get the elements in a nice predictable order (so you can compare the lists afterwards, for example).

>>> s = set([1, 2, 3, 4, 5])
>>> sorted(s)
[1, 2, 3, 4, 5]

Of course, the set elements have to be sortable for this to work. You can’t sort complex numbers (see gnibbler’s comment).
In Python 3, you also can’t sort any set with mixed data types, e.g. set([1, 2, 'string']).

You can use sorted(s, key=str), but it may not be worth the trouble in these cases.

Answered By: Petr Viktorin

Answer 3

>>> a = [1, 2, 3, 4, 2, 3]
>>> b = set(a)
>>> b
set([1, 2, 3, 4])
>>> c = list(b)
>>> c
[1, 2, 3, 4]
>>>

Answered By: sam

How to get a list from a set?

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