return a list of items without any elements with the same value next to each other

Use existing libraries to perform that task, like itertools.groupby

import itertools

def unique_in_order(iterable):
    return [k for k,_ in itertools.groupby(iterable)]

print(unique_in_order('AAAABBBCCDAABBB')) # ['A', 'B', 'C', 'D', 'A', 'B']
print(unique_in_order(['A']))  # ['A']

With the default group key, groupby groups identical consecutive elements, yielding tuples with the value and the group of values (that we ignore here, we just need the key)