Converting a set into list

[Steven D'Aprano]

On Mon, 16 May 2011 00:05:44 +0800, TheSaint wrote:

> Chris Torek wrote:
> 
>> >>> x = ['three', 'one', 'four', 'one', 'five'] x
>> ['three', 'one', 'four', 'one', 'five']
>> >>> list(set(x))
>> ['four', 'five', 'three', 'one']
> 
> Why one *"one"* has purged out?
> Removing double occurences in a list?

Break the operation up into two steps instead of one:


>>> x = ['three', 'one', 'four', 'one', 'five']
>>> s = set(x)
>>> print s
set(['four', 'five', 'three', 'one'])
>>> list(s)
['four', 'five', 'three', 'one']


Once an element is already in a set, adding it again is a null-op:


>>> s = set()
>>> s.add(42)
>>> s.add(42)
>>> s.add(42)
>>> print s
set([42])




-- 
Steven