from itertools import chain
lis = [['a','1','2','3','4'],['b','5','6','7','8'],['c','9','10','11','12'],['d','13','14','15','16']]
it = iter(lis)
print list( chain.from_iterable([map(list,zip(x,next(it))) for x in it]))
ZnJvbSBpdGVydG9vbHMgaW1wb3J0IGNoYWluCmxpcyA9IFtbJ2EnLCcxJywnMicsJzMnLCc0J10sWydiJywnNScsJzYnLCc3JywnOCddLFsnYycsJzknLCcxMCcsJzExJywnMTInXSxbJ2QnLCcxMycsJzE0JywnMTUnLCcxNiddXQppdCA9IGl0ZXIobGlzKQpwcmludCBsaXN0KCBjaGFpbi5mcm9tX2l0ZXJhYmxlKFttYXAobGlzdCx6aXAoeCxuZXh0KGl0KSkpIGZvciB4IGluIGl0XSkp
[['a', 'b'], ['1', '5'], ['2', '6'], ['3', '7'], ['4', '8'], ['c', 'd'], ['9', '13'], ['10', '14'], ['11', '15'], ['12', '16']]