004、python 运算符和字符串操作

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本节内容：

一、python运算符：算术、赋值、比较运算符、逻辑运算符。

二、python 字符串操作：

　　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)

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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)

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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)

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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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不同数据类型可以 == 比较， > 或 < 比较报错。

a = 12
b = 'hello'

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

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

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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)

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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'))
# print(var1.index('w'))  #  报错 ValueError: substring not found

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.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)

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
请输入价格：12.5
请输入重量：5.7
71.25

Process finished with exit code 0

View Code

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)

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执行结果如下：

D:\SkyWorkSpace\WorkSpace\Pytest\Temp\day06\venv\Scripts\python.exe D:/SkyWorkSpace/WorkSpace/Pytest/Temp/day06/test_demo/test_06.py
o
python cainiao 666

Process finished with exit code 0

View Code

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