a = [1,2]
c = a + [3,4]
print(c)
输入出：[1, 2, 3, 4]
a = [1,2]
c = a + [3,4]
#就地加
a += [3,4]
print(a)
输出结果：
[1, 2, 3, 4]
a = [1,2]
# c = a + (3,4)
#就地加
a += [3,4]
print(a)
运行提示错误：
TypeError: can only concatenate list (not "tuple") to list
1 a = [1,2]
2 a.append((1,2))
3 print(a)
4 运行结果：
5 [1, 2, (1, 2)]
a = [1,2]
a.extend([5,6,7])
print(a)
运行结果：
[1, 2, 5, 6, 7]
