Removing duplicates from a list

[Peter Otten]

Rubinho wrote:

> I've a list with duplicate members and I need to make each entry
> unique.
> 
> I've come up with two ways of doing it and I'd like some input on what
> would be considered more pythonic (or at least best practice).
> 
> Method 1 (the traditional approach)
> 
> for x in mylist:
>     if mylist.count(x) > 1:
>         mylist.remove(x)

That would be an odd tradition:

>>> mylist = [1, 2, 1, 3, 2, 3]
>>> for x in mylist:
...     if mylist.count(x) > 1:
...             mylist.remove(x)
...
>>> mylist
[2, 1, 2, 3] # oops!

See "Unexpected Behavior Iterating over a Mutating Object" 
http://mail.python.org/pipermail/python-list/2005-September/298993.html
thread for the most recent explanation.

Rather, the traditional approach for an algorithmic problem in Python is to
ask Tim Peters, see his recipe at
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560/
(which predates Python's set class).

Peter