python - One-liner to remove duplicates, keep ordering of list

I have the following list:

['Herb', 'Alec', 'Herb', 'Don']

I want to remove duplicates while keeping the order, so it would be :

['Herb', 'Alec', 'Don']

Here is how I would do this verbosely:

l_new = []
for item in l_old:
    if item not in l_new: l_new.append(item)

Is there a way to do this in a single line?

Answer

You could use an OrderedDict, but I suggest sticking with your for-loop.

>>> from collections import OrderedDict

>>> data = ['Herb', 'Alec', 'Herb', 'Don']
>>> list(OrderedDict.fromkeys(data))
['Herb', 'Alec', 'Don']

Just to reiterate: I seriously suggest sticking with your for-loop approach, and use a set to keep track of already seen items:

>>> data = ['Herb', 'Alec', 'Herb', 'Don']
>>> seen = set()
>>> unique_data = []

>>> for x in data:
...     if x not in seen:
...         unique_data.append(x)
...         seen.add(x)
...
>>> unique_data
['Herb', 'Alec', 'Don']

And in case you just want to be wacky (seriously don't do this):

>>> [t[0] for t in sorted(dict(zip(reversed(data), range(len(data), -1, -1))).items(), key=lambda t:t[1])]
['Herb', 'Alec', 'Don']