改写Python中嵌套的for循环

nested_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# 嵌套的for循环
flattened_list = []
for sublist in nested_list:
    for item in sublist:
        flattened_list.append(item)

# 使用列表推导式改写
flattened_list = [item for sublist in nested_list for item in sublist]

print(flattened_list)

nested_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# 嵌套的for循环
flattened_list = []
for sublist in nested_list:
    for item in sublist:
        flattened_list.append(item)

# 使用生成器表达式改写
flattened_list = (item for sublist in nested_list for item in sublist)

print(list(flattened_list))