在python中组合列表，但保持顺序

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined_list = list1 + list2
print(combined_list)  # 输出: [1, 2, 3, 4, 5, 6]

list1 = [1, 2, 3]
list2 = [4, 5, 6]
list1.extend(list2)
print(list1)  # 输出: [1, 2, 3, 4, 5, 6]

lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
combined_list = [item for sublist in lists for item in sublist]
print(combined_list)  # 输出: [1, 2, 3, 4, 5, 6, 7, 8, 9]

import itertools

list1 = [1, 2, 3]
list2 = [4, 5, 6]
combined_list = list(itertools.chain(list1, list2))
print(combined_list)  # 输出: [1, 2, 3, 4, 5, 6]