list1 = ['a', 'b', 'c', 'd']
list2 = [['1', '2', '3'], ['4', '5', '6'], ['7', '8']]
req_len = len(list1)
result = [list1] + [(org + ['' * (req_len - len(org))]) for org in list2]
print(result)
Best way to merge a 2d list and a 1d list in Python?