Python 复习 Part2

I. String

1.definition:a sequence of case sensitive(大小写敏感) characters

2.Enclose in quotation marks or single quotes

3.Concatenate(附加)

a="hello"
b="world"
c=a+" "+b

repeat

d=a*3
#variable        value
#d                "hellohellohello"

4.len()is a function used to retrieve the length of a string in the parentheses

5.indexing(下标)

6.slice(切片)strings using [start:stop:step]

Get characters at start，up to and including stop-1，taking every step characters

 If give two numbers,[start:stop], step=1 by default

 If give one number, you are back to indexing for the character at one location (prev slide)

(其实就是在 $[start,stop)$ 注意是左闭右开区间中，按照步长step间隔地取字符，给了step和stop默认情况下step=1,即每个字符都取出来，不跳过。给了一个数，就会倒过来取，从-1开始)

Python 3.13.7 (tags/v3.13.7:bcee1c3, Aug 14 2025, 14:15:11) [MSC v.1944 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> s="immersive programming"
>>> s[::-1]
'gnimmargorp evisremmi'
>>> s[0:len(s):-1]
''
>>> s[::1]
'immersive programming'
>>> s[::2]
'imriepormig'
>>> s[::-2]
'gimropeirmi'
>>>

7.immutable(不可变)