Question

所以代码是：

X = range(4, 7)
Y = range(2)
X[2] = Y
print X[2][0]
print X[2][1]

X[2][0] = 9
print Y[0]

输出

0
1
9

代码究竟在做什么来获得输出？如果代码看起来像

X = range(4, 7)
print X[-1]

然后输出会是什么，因为我对负值的作用感到困惑。

Answer 1

>>> X = range(4, 7)  # List of number from 4 to 6
>>> Y = range(2)     # List of number from 0 to 1
>>> X
[4, 5, 6]
>>> Y
[0, 1]
>>> X[2] = Y         # Stored 'Y' at X[2] in place of '6'
                     # X[2]  is referencing Y  
>>> X
[4, 5, [0, 1]]
>>> print X[2][0]    # '0'th index of X[2] i.e Y[0] 
0
>>> print X[2][1]    # '1'th index of X[2] i.e Y[1]
1
>>> X[2][0] = 9      # Set '0'th index of X[2] i.e Y[0] as 9
>>> Y[0]
9
>>> Y
[9, 1]
>>> X
[4, 5, [9, 1]]

现在回答您与negative index相关的另一个问题。 -i作为索引represnt i来自最后一个元素。例如：

>>> X = range(4, 7)
>>> X
[4, 5, 6]
>>> X[-1]    # 1st element from last
6
>>> X[-3]    # 3rd element from last
4

Answer 2

如果一个字符串的值为x =“Hello”，则从左到右为这些字符分配值0,1,2,3,4，从右到左分配-1,-2,-3,-4,-5，如果你说

print x[-1]

如果你说

，它将返回'o'

print x[0]

它将返回'H'，希望澄清。

用嵌套范围解释此代码的输出

2 个答案: