python best way to concatenate lists code example

Example 1: add two list in python

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]

list1.extend(list2)
print(list1)

Example 2: merge lists in list python

import itertools
a = [['a','b'], ['c']]
print(list(itertools.chain.from_iterable(a)))