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# 004、python 运算符 和 字符串操作

4小时前 1次浏览

a、索引取值、切片

b、拼接、转义

c、常见操作

d、格式化输出

1a、算术运算   +     —     *      /     %

```# -*- coding:utf-8 -*-
# @Author:  Sky
# @Email:   2780619724@qq.com
# @Time:    2021/7/22 21:56

a = 15
b = 2
c = 3.1415

# 算术运算——加法
print(a + b)
print(a + c)

# 算术运算——减法
print(a - b)

# 算术运算——乘法
print(a * b)

# 算术运算——除法
print(a / b)

# 算术运算——取模运算
print(a % b)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
17
18.1415
13
30
7.5
1

Process finished with exit code 0```

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### 1b、赋值运算：   =      +=      -=     *=    %=

```# -*- coding:utf-8 -*-
# @Author:  Sky
# @Email:   2780619724@qq.com
# @Time:    2021/7/22 21:56

# a = 15
# b = 2
# c = 3.1415
#
# # 算术运算——加法
# print(a + b)
# print(a + c)
#
# # 算术运算——减法
# print(a - b)
#
# # 算术运算——乘法
# print(a * b)
#
# # 算术运算——除法
# print(a / b)
#
# # 算术运算——取模运算
# print(a % b)

a = 15
b = 2
c = 3.1415

# = 赋值运算
d = 15 % 2
print(d)

# += 累加赋值
b += a
print(b)

# -= 累减赋值
a -= b
print(a)

# *= 累乘赋值
c *= b
print(c)

e = 7
f = 2

e %= f
print(e)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
1
17
-2
53.4055
1

Process finished with exit code 0```

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### 1c、比较运算符     ==   、 !=、  > 、 >=  、 < 、 <=

```#  比较运算符     ==   、 !=、  > 、 >=  、 < 、 <=
a = 3
b = 4
c = 'hello'
d = 'world'

print(a == b)
print(c == d)
print(b == c)

print(a != b)
print(a > b)
print(a >= b)
print(a < b)
print(a <= b)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
False
False
False
True
False
False
True
True

Process finished with exit code 0```

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```a = 12
b = 'hello'

print(type(a))
print(type(b))

c = (a == b)
d = (a > b)
print(c)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
<class 'int'>
<class 'str'>
Traceback (most recent call last):
File "D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py", line 89, in <module>
d = (a > b)
TypeError: '>' not supported between instances of 'int' and 'str'

Process finished with exit code 1```

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### 1d、逻辑运算符   and(与) 、 or(或)、  not(非)

```#  and(与) 、 or(或)、  not(非)
a = True
b = False

print(a and b)
print(a or b)
print(not a)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
False
True
False

Process finished with exit code 0```

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### 2a、字符串切片

字符串切片，[1:3]  包头不包尾  [1:3)

```var1 = 'Hello World!'
var2 = "Runoob"

#  索引值以 0 为开始值，-1 为从末尾的开始位置。
print(var1[:3])
print(var1[0:3])

print(var1[1:])
print(var1[1:20])

print(var1[1::2])       # 截取步长
print(var1[::-1])       # 逆序
print(var1[:])          # 获取所有

print(var1[-1])         # 取最后一个字符```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
Hel
Hel
ello World!
ello World!
el ol!
!dlroW olleH
Hello World!
!

Process finished with exit code 0```

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### 2b、字符串常见操作

全部大写：  upper()

全部小写：  lower()

查找：　　 find(子字符串)   返回匹配到的第一个索引 ，未查到返回  -1

替换：　　 replace(旧，新，[替换的次数])

index()：   未查到报错， 与 find()  不一样

```var1 = 'Hello World!'
var2 = 'Hello World! Hello World! Hello World!'

print(var1.upper())
print(var2.lower())

print(var1.find('w'))
print(var1.find('W'))

print(var2.replace('World', 'java', 2))     # 替换2个

print(var1.index('W'))

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
HELLO WORLD!
hello world! hello world! hello world!
-1
6
Hello java! Hello java! Hello World!
6

Process finished with exit code 0```

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### 随堂练习：

```#  数据类型强制转换
price = float(input('请输入价格：'))
weight = float(input('请输入重量：'))
result = price*weight
print(result)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py

71.25

Process finished with exit code 0```

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```str1 = 'python cainiao 666'
#  找出第5个字符
#  复制一份字符串，保存为 str_two（使用赋值运算符）

print(str1[4])
str_two = str1
print(str_two)```

View Code

```D:SkyWorkSpaceWorkSpacePytestTempday06venvScriptspython.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
o
python cainiao 666

Process finished with exit code 0```

View Code