How can I remove duplicate words in a string with Python?

Following example:

string1 = "calvin klein design dress calvin klein"

How can I remove the second two duplicates "calvin" and "klein"?

The result should look like

string2 = "calvin klein design dress"

only the second duplicates should be removed and the sequence of the words should not be changed!

Answer

def unique_list(l):
    ulist = []
    [ulist.append(x) for x in l if x not in ulist]
    return ulist

a="calvin klein design dress calvin klein"
a=' '.join(unique_list(a.split()))