# sublists_flatten.py

# sublists_flatten.py

L1 = [1, 2, 3]
L2 = [4, 5, [], 6]
L3 = [7, 8, 9, 'z']
L = [L1, L2, L3]

s=[x for y in L for x in y]
print s

### ... or even better... ###

print sum(L,[])