>>> import itertools
>>> [i[0] for i in itertools.groupby([1,2,2,3,3,3,2,2])]
[1, 2, 3, 2]
Или:
>>> def f(l):
... r = []
... last = None
... for i in l:
... if i != last:
... r.append(i)
... last = i
... return r
...
>>> f([1,2,2,3,3,3,4,4,2,2])
[1, 2, 3, 4, 2]