前言

Python語(yǔ)言處理字符串、數(shù)組類的問題時(shí)有一定概率需要使用切片方法，比如：Leetcode_5。
學(xué)習(xí)官方解法時(shí)發(fā)現(xiàn)切片的索引可以超出字符串或數(shù)組最大索引值，此時(shí)編譯器不會(huì)報(bào)錯(cuò)。
歡迎大佬留言說明這種情況的具體原因，本文只進(jìn)行一些情況的簡(jiǎn)單測(cè)試。

實(shí)例代碼

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

發(fā)現(xiàn)結(jié)果為123，編譯器沒有報(bào)錯(cuò)。而當(dāng)直接使用a[5]時(shí)即報(bào)錯(cuò)string index out of range。下面是測(cè)試結(jié)果。

測(cè)試代碼（字符串）

a = "1234567890"
a1 = a[:]
a2 = a[:len(a)]
a3 = a[:15]
a4 = a[16:16]
a5 = a[:2]

運(yùn)行結(jié)果：

This is the id of 'a' :? 2707772994160
This 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' :?

This is the id of 'a5' :? 2707773122544
This is the type of 'a5' :? <class 'str'>
This is the value of 'a5' :? 12

值得注意的地方：

• 若切片后結(jié)果與原來相同，則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)。
• 若切片后結(jié)果與原來不同，則新字符串指向新的物理地址(a5)。
• 若當(dāng)前切片索引范圍內(nèi)不存在合法數(shù)值，則返回相應(yīng)類型的空值(a4)。

測(cè)試代碼（數(shù)組）

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：

• 數(shù)組切片操作必定指向新的物理地址。
• 若當(dāng)前切片索引范圍內(nèi)不存在合法數(shù)值，則返回相應(yīng)類型的空值(b4)。

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