[z for b in a for c in b for d in c ... for z in y]
Which would be like having this regular for-loop:
 
for b in a:
    for c in b:
        for d in c:
            ...
                for z in y:
                    # have z

list(set(sorted([v for i in [dict(parser.items(x)) for x in parser.sections()] for k,v in i.items() if k.startswith('group')])))

vec = [[1,2,3], [4,5,6], [7,8,9]]
print [num for elem in vec for num in elem]      <----- this
 
>>> [1, 2, 3, 4, 5, 6, 7, 8, 9]