Python 切片索引越界的问题(数组下标越界)

前言

python语言处理字符串、数组类的问题时有一定概率需要使用切片方法，比如：Leetcode_5。

学习官方解法时发现切片的索引可以超出字符串或数组最大索引值，此时编译器不会报错。

欢迎大佬留言说明这种情况的具体原因，本文只进行一些情况的简单测试。

实例代码

a = '123'
b = a[:5]
print(b)

发现结果为123，编译器没有报错。而当直接使用a[5]时即报错string index out of range。下面是测试结果。

测试代码（字符串）

a = "1234567890"
a1 = a[:]
a2 = a[:l编程客栈en(a)]
a3 = a[:15]
a4 = a[16:16]
a5 = a[:2]

运行结果：

This is the id of 'a' : 2707772994160

This 编程客栈is the type of 'a' : <class 'str'>

This is the value of 'a' : 1234567890

This is the id of 'a1' : 2707772994160

This is the type of 'a1' : <class 'str'>

This is the value of 'a1' : 1234567890

This is the id of 'a2' : 2707772994160

This is the type of 'a2' : <class 'str'>

This is the value of 'a2' : 1234567890

This is the id of 'a3' : 2707772994160

This is the type of 'a3' : <class 'str'>

This is the value of 'a3' : 1234567890

This is the id of 'a4' : 2707740774832

This is the type of 'a4' : <class 'str'>

This is the value of 'a4' :

Th编程客栈is is the id of 'a5' : 2707773122544

This is the type of 'a5' : <class 'str'>www.cppcns.com;

This is the value of 'a5' : 12

值得注意的地方：

• 若切片后结果与原来相同http://www.cppcns.com，则新字符串所指向的物理地址就是原字符串的物理地址(a1、a2、a3)。
• 若切片后结果与原来不同，则新字符串指向新的物理地址(a5)。
• 若当前切片索引范围内不存在合法数值，则返回相应类型的空值(a4)。

测试代码（数组）

b = [1, 2, 3, 4, 5]
b1 = b[:]
b2 = b[:len(b)]
b3 = b[:15]
b4 = b[16:16]
b5 = b[:2]

This is the id of 'b' : 2260784433096

This is the type of 'b' : <class 'list'>

This is the value of 'b' : [1, 2, 3, 4, 5]

This is the id of 'b1' : 2260784432456

This is the type of 'b1' : <class 'list'>

This is the value of 'b1' : [1, 2, 3, 4, 5]

This is the id of 'b2' : 2260784470920

This is the type of 'b2' : <class 'list'>

This is the value of 'b2' : [1, 2, 3, 4, 5]

This is the id of 'b3' : 2260784534280

This is the type of 'b3' : <class 'list'>

This is the value of 'b3' : [1, 2, 3, 4, 5]

This is the id of 'b4' : 2260784471432

This is the type of 'b4' : <class 'list'>

This is the value of 'b4' : []

This is the id of 'b5' : 2260784231944

This is the type of 'b5' : <class 'list'>

This is the value of 'b5' : [1, 2]

值得注意的地方：

• 数组切片操作必定指向新的物理地址。
• 若当前切片索引范围内不存在合法数值，则返回相应类型的空值(b4)。

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