Different methods to merge two lists.

merge_lists.py

import random
import itertools
import operator
import functools
import collections

def extend(list1_list2):
    list1, list2 = list1_list2
    merged_list = []
    merged_list.extend(list1)
    merged_list.extend(list2)
    return merged_list


def unpacking(list1_list2):
    list1, list2 = list1_list2
    merged_list = [*list1, *list2]
    return merged_list


def chaining(list1_list2):
    list1, list2 = list1_list2
    return list(itertools.chain(list1, list2))


def plus_operator(list1_list2):
    list1, list2 = list1_list2
    return list1 + list2


def iadd(list1_list2):
    list1, list2 = list1_list2
    list1 = list1.copy()
    list1 += list2
    return list1


def dict_fromkeys(list1_list2):
    # remove duplicates
    # order not preserved
    list1, list2 = list1_list2
    return list(dict.fromkeys(list1 + list2))


def reduce_add_operator(list1_list2):
    list1, list2 = list1_list2
    return functools.reduce(operator.add, [list1, list2])


def sum_method(list1_list2):
    list1, list2 = list1_list2
    return sum([list1, list2], [])


def ordered_dict_fromkeys(list1_list2):
    # remove duplicates
    # preserve order
    list1, list2 = list1_list2
    return list(collections.OrderedDict.fromkeys(list1 + list2))


def chaining_from_iterable(list1_list2):
    list1, list2 = list1_list2
    return list(itertools.chain.from_iterable([list1 + list2]))


def generators(list1_list2):
    list1, list2 = list1_list2

    def inner(list1, list2):
        yield from list1
        yield from list2

    return list(inner(list1, list2))


def list_comprehension(list1_list2):
    list1, list2 = list1_list2
    return [item for list_ in [list1, list2] for item in list_]


def two_for_loops(list1_list2):
    list1, list2 = list1_list2
    merged_list = []
    for element in list1:
        merged_list.append(element)
    for element in list2:
        merged_list.append(element)
    return merged_list

list1_list2 has the following schema:

list1_list2 = [list1, list2]
# example
list1_list2 = [[1, 3, 4], [5, 2]]