def unify seq unique for in seq if not in unique unique append return

def unify(seq):
    unique = []
    for x in seq:
        if x not in unique:
            unique.append(x)
    return unique
    
In [1]: l = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5]

In [2]: set(l)
Out[2]: set([1, 2, 3, 4, 5])

In [3]: unify(l)
Out[3]: [1, 2, 3, 4, 5]