get rid of duplicate elements in list without set

Aaron Brady castironpi at
Sat Mar 21 01:12:51 CET 2009

On Mar 20, 5:07 pm, Michael Spencer <m... at> wrote:
> Alexzive wrote:
> And, if you really want, you can get the body of this into 1-line, noting that
> seen.add returns None, so the expression (item in seen or seen.add(item))
> evaluates to True if item is in seen, or None (and item is added to seen) if not.
>   >>> seen = set()
>   >>> B=  [item for item in A if not (item in seen or seen.add(item))]
>   >>> B
>   [1, 2, 3, 4]

IYO in your opinion, is '... or seen.add(item) is None' more or less

You might even want '... or ( lambda x: False )( seen.add( item ) )'.

Or: '... or seen.add(item) and False'.

This preserves order.

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