Python a, b = b, a背后的故事
a = [1,2,3,4,5,6]
x = 0
a[x] = 1
a[a[x]] = 2
a[x], a[a[x]] = a[a[x]], a[x] # 实质执行了 xxx = a[a[x]], a[x] ; a[x], a[a[x]] = xxx
print(a) # [2, 2, 1, 4, 5, 6]
c, d = 1, 2
c, d = d, c + d # 实质执行了 xxx = d, c + d ; c,d = xxx
print(c, d) # 2 3
种一棵树最好的时间是十年前,其次是现在。