how can I add a list of lists to a list in python

Question

am trying to add a list of lists to a list

a = [['xx',''ee', 'yy'], [1,2,3]]

existing = [['zz', 'ss', 'ww'], [4,5,6]]

what is the best way add elements of a into the existing list

expected = [['zz', 'ss', 'ww'], [4,5,6], ['xx',''ee', 'yy'], [1,2,3]]

Answer 1

Either use extend or + for concatenation as:

a = [['xx','ee', 'yy'], [1,2,3]]
b = [['zz', 'ss', 'ww'], [4,5,6]]
b = b + a
print(b)

a = [['xx','ee', 'yy'], [1,2,3]]
b = [['zz', 'ss', 'ww'], [4,5,6]]
b.extend(a)
print(b)

Answer 2

expected = existing + a
print(expected)

output is :

[['zz', 'ss', 'ww'], [4, 5, 6], ['xx', 'ee', 'yy'], [1, 2, 3]]