Python

Python 基础教程 Python 基础教程 Python 简介 Python 环境搭建 Python 中文编码 Python 基础语法 Python 变量类型 Python 运算符 Python 条件语句 Python 循环语句 Python While循环语句 Python for 循环语句 Python 循环嵌套 Python break 语句 Python continue 语句 Python pass 语句 Python 数字 Python 字符串 Python 列表(Lists) Python 元组 Python 字典(Dictionary) Python 日期和时间 Python 函数 Python 模块 Python 文件I/O Python 异常处理 Python 高级教程 Python 面向对象 Python正则表达式 Python CGI编程 python操作mysql数据库 Python使用SMTP发送邮件 Python 多线程 Python XML解析 python GUI编程(Tkinter) Python2.x与3.x版本区别 Python IDE Python JSON Python 3 Python3 教程 Python3 基础语法 Python3 基本数据类型 Python 解释器 Python 注释 Python 数字运算 Python 字符串 Python 列表 Python 编程第一步 Python 条件控制 Python 循环 Python 函数 Python 数据结构 Python 模块 Python 输入和输出 Python 错误和异常 Python 类 Python 标准库概览 Python3 实例 Python3 正则表达式 Python3 CGI编程 Python3 MySQL Python3 网络编程 Python3 SMTP发送邮件 Python3 多线程 Python3 XML解析 Python3 JSON Python3 日期和时间 Django Django 安装 Django 创建第一个项目 Django 模板 Django 模型 Django 表单 Django Admin 管理工具 Django Nginx+uwsgi 安装配置

Python 运算符

Python运算符

什么是运算符？

本章节主要说明Python的运算符。举个简单的例子 4 +5 = 9 。例子中，4和5被称为操作数，"+"号为运算符。

Python语言支持以下类型的运算符:

算术运算符
比较（关系）运算符
赋值运算符
逻辑运算符
位运算符
成员运算符
身份运算符
运算符优先级

接下来让我们一个个来学习Python的运算符。

Python算术运算符

以下假设变量a为10，变量b为20：

运算符	描述	实例
+	加 - 两个对象相加	a + b 输出结果 30
-	减 - 得到负数或是一个数减去另一个数	a - b 输出结果 -10
*	乘 - 两个数相乘或是返回一个被重复若干次的字符串	a * b 输出结果 200
/	除 - x除以y	b / a 输出结果 2
%	取模 - 返回除法的余数	b % a 输出结果 0
**	幂 - 返回x的y次幂	a**b 为10的20次方，输出结果 100000000000000000000
//	取整除 - 返回商的整数部分	9//2 输出结果 4 , 9.0//2.0 输出结果 4.0

以下实例演示了Python所有算术运算符的操作：

#!/usr/bin/python

a = 21
b = 10
c = 0

c = a + b
print "Line 1 - Value of c is ", c

c = a - b
print "Line 2 - Value of c is ", c 

c = a * b
print "Line 3 - Value of c is ", c 

c = a / b
print "Line 4 - Value of c is ", c 

c = a % b
print "Line 5 - Value of c is ", c

a = 2
b = 3
c = a**b 
print "Line 6 - Value of c is ", c

a = 10
b = 5
c = a//b 
print "Line 7 - Value of c is ", c

以上实例输出结果：

Line 1 - Value of c is 31
Line 2 - Value of c is 11
Line 3 - Value of c is 210
Line 4 - Value of c is 2
Line 5 - Value of c is 1
Line 6 - Value of c is 8
Line 7 - Value of c is 2

Python比较运算符

以下假设变量a为10，变量b为20：

运算符	描述	实例
==	等于 - 比较对象是否相等	(a == b) 返回 False。
!=	不等于 - 比较两个对象是否不相等	(a != b) 返回 true.
<>	不等于 - 比较两个对象是否不相等	(a <> b) 返回 true。这个运算符类似 != 。
>	大于 - 返回x是否大于y	(a > b) 返回 False。
<	小于 - 返回x是否小于y。所有比较运算符返回1表示真，返回0表示假。这分别与特殊的变量True和False等价。注意，这些变量名的大写。	(a < b) 返回 true。
>=	大于等于 - 返回x是否大于等于y。	(a >= b) 返回 False。
<=	小于等于 - 返回x是否小于等于y。	(a <= b) 返回 true。

以下实例演示了Python所有比较运算符的操作：

#!/usr/bin/python

a = 21
b = 10
c = 0

if ( a == b ):
   print "Line 1 - a is equal to b"
else:
   print "Line 1 - a is not equal to b"

if ( a != b ):
   print "Line 2 - a is not equal to b"
else:
   print "Line 2 - a is equal to b"

if ( a <> b ):
   print "Line 3 - a is not equal to b"
else:
   print "Line 3 - a is equal to b"

if ( a < b ):
   print "Line 4 - a is less than b" 
else:
   print "Line 4 - a is not less than b"

if ( a > b ):
   print "Line 5 - a is greater than b"
else:
   print "Line 5 - a is not greater than b"

a = 5;
b = 20;
if ( a <= b ):
   print "Line 6 - a is either less than or equal to  b"
else:
   print "Line 6 - a is neither less than nor equal to  b"

if ( b >= a ):
   print "Line 7 - b is either greater than  or equal to b"
else:
   print "Line 7 - b is neither greater than  nor equal to b"

以上实例输出结果：

Line 1 - a is not equal to b
Line 2 - a is not equal to b
Line 3 - a is not equal to b
Line 4 - a is not less than b
Line 5 - a is greater than b
Line 6 - a is either less than or equal to b
Line 7 - b is either greater than or equal to b

Python赋值运算符

以下假设变量a为10，变量b为20：

运算符	描述	实例
=	简单的赋值运算符	c = a + b 将 a + b 的运算结果赋值为 c
+=	加法赋值运算符	c += a 等效于 c = c + a
-=	减法赋值运算符	c -= a 等效于 c = c - a
*=	乘法赋值运算符	c = a 等效于 c = c a
/=	除法赋值运算符	c /= a 等效于 c = c / a
%=	取模赋值运算符	c %= a 等效于 c = c % a
**=	幂赋值运算符	c = a 等效于 c = c a
//=	取整除赋值运算符	c //= a 等效于 c = c // a

以下实例演示了Python所有赋值运算符的操作：

#!/usr/bin/python

a = 21
b = 10
c = 0

c = a + b
print "Line 1 - Value of c is ", c

c += a
print "Line 2 - Value of c is ", c 

c *= a
print "Line 3 - Value of c is ", c 

c /= a 
print "Line 4 - Value of c is ", c 

c  = 2
c %= a
print "Line 5 - Value of c is ", c

c **= a
print "Line 6 - Value of c is ", c

c //= a
print "Line 7 - Value of c is ", c

以上实例输出结果：

Line 1 - Value of c is 31
Line 2 - Value of c is 52
Line 3 - Value of c is 1092
Line 4 - Value of c is 52
Line 5 - Value of c is 2
Line 6 - Value of c is 2097152
Line 7 - Value of c is 99864

Python位运算符

按位运算符是把数字看作二进制来进行计算的。Python中的按位运算法则如下：

运算符	描述	实例
&	按位与运算符	(a & b) 输出结果 12 ，二进制解释： 0000 1100
\|	按位或运算符	(a \| b) 输出结果 61 ，二进制解释： 0011 1101
^	按位异或运算符	(a ^ b) 输出结果 49 ，二进制解释： 0011 0001
~	按位取反运算符	(~a ) 输出结果 -61 ，二进制解释： 1100 0011，在一个有符号二进制数的补码形式。
<<	左移动运算符	a << 2 输出结果 240 ，二进制解释： 1111 0000
>>	右移动运算符	a >> 2 输出结果 15 ，二进制解释： 0000 1111

以下实例演示了Python所有位运算符的操作：

#!/usr/bin/python

a = 60            # 60 = 0011 1100 
b = 13            # 13 = 0000 1101 
c = 0

c = a & b;        # 12 = 0000 1100
print "Line 1 - Value of c is ", c

c = a | b;        # 61 = 0011 1101 
print "Line 2 - Value of c is ", c

c = a ^ b;        # 49 = 0011 0001
print "Line 3 - Value of c is ", c

c = ~a;           # -61 = 1100 0011
print "Line 4 - Value of c is ", c

c = a << 2;       # 240 = 1111 0000
print "Line 5 - Value of c is ", c

c = a >> 2;       # 15 = 0000 1111
print "Line 6 - Value of c is ", c

以上实例输出结果：

Line 1 - Value of c is 12
Line 2 - Value of c is 61
Line 3 - Value of c is 49
Line 4 - Value of c is -61
Line 5 - Value of c is 240
Line 6 - Value of c is 15

Python逻辑运算符

Python语言支持逻辑运算符，以下假设变量a为10，变量b为20：

运算符	描述	实例
and	布尔"与" - 如果x为False，x and y返回False，否则它返回y的计算值。	(a and b) 返回 true。
or	布尔"或" - 如果x是True，它返回True，否则它返回y的计算值。	(a or b) 返回 true。
not	布尔"非" - 如果x为True，返回False。如果x为False，它返回True。	not(a and b) 返回 false。

以下实例演示了Python所有逻辑运算符的操作：

#!/usr/bin/python

a = 10
b = 20
c = 0

if ( a and b ):
   print "Line 1 - a and b are true"
else:
   print "Line 1 - Either a is not true or b is not true"

if ( a or b ):
   print "Line 2 - Either a is true or b is true or both are true"
else:
   print "Line 2 - Neither a is true nor b is true"


a = 0
if ( a and b ):
   print "Line 3 - a and b are true"
else:
   print "Line 3 - Either a is not true or b is not true"

if ( a or b ):
   print "Line 4 - Either a is true or b is true or both are true"
else:
   print "Line 4 - Neither a is true nor b is true"

if not( a and b ):
   print "Line 5 - Either a is not true or b is  not true or both are not true"
else:
   print "Line 5 - a and b are true"

以上实例输出结果：

Line 1 - a and b are true
Line 2 - Either a is true or b is true or both are true
Line 3 - Either a is not true or b is not true
Line 4 - Either a is true or b is true or both are true
Line 5 - Either a is not true or b is  not true or both are not true

Python成员运算符

除了以上的一些运算符之外，Python还支持成员运算符，测试实例中包含了一系列的成员，包括字符串，列表或元组。

运算符	描述	实例
in	如果在指定的序列中找到值返回True，否则返回False。	x 在 y序列中 , 如果x在y序列中返回True。
not in	如果在指定的序列中没有找到值返回True，否则返回False。	x 不在 y序列中 , 如果x不在y序列中返回True。

以下实例演示了Python所有成员运算符的操作：

#!/usr/bin/python

a = 10
b = 20
list = [1, 2, 3, 4, 5 ];

if ( a in list ):
   print "Line 1 - a is available in the given list"
else:
   print "Line 1 - a is not available in the given list"

if ( b not in list ):
   print "Line 2 - b is not available in the given list"
else:
   print "Line 2 - b is available in the given list"

a = 2
if ( a in list ):
   print "Line 3 - a is available in the given list"
else:
   print "Line 3 - a is not available in the given list"

以上实例输出结果：

Line 1 - a is not available in the given list
Line 2 - b is not available in the given list
Line 3 - a is available in the given list

Python身份运算符

身份运算符用于比较两个对象的存储单元

运算符	描述	实例
is	is是判断两个标识符是不是引用自一个对象	x is y, 如果 id(x) 等于 id(y) , is 返回结果 1
is not	is not是判断两个标识符是不是引用自不同对象	x is not y, 如果 id(x) 不等于 id(y). is not 返回结果 1

以下实例演示了Python所有身份运算符的操作：

#!/usr/bin/python

a = 20
b = 20

if ( a is b ):
   print "Line 1 - a and b have same identity"
else:
   print "Line 1 - a and b do not have same identity"

if ( id(a) == id(b) ):
   print "Line 2 - a and b have same identity"
else:
   print "Line 2 - a and b do not have same identity"

b = 30
if ( a is b ):
   print "Line 3 - a and b have same identity"
else:
   print "Line 3 - a and b do not have same identity"

if ( a is not b ):
   print "Line 4 - a and b do not have same identity"
else:
   print "Line 4 - a and b have same identity"

以上实例输出结果：

Line 1 - a and b have same identity
Line 2 - a and b have same identity
Line 3 - a and b do not have same identity
Line 4 - a and b do not have same identity

Python运算符优先级

以下表格列出了从最高到最低优先级的所有运算符：

运算符	描述
**	指数 (最高优先级)
~ + -	按位翻转, 一元加号和减号 (最后两个的方法名为 +@ 和 -@)
* / % //	乘，除，取模和取整除
+ -	加法减法
>> <<	右移，左移运算符
&	位 ‘AND‘
^ \|	位运算符
<= < > >=	比较运算符
<> == !=	等于运算符
= %= /= //= -= += = *=	赋值运算符
is is not	身份运算符
in not in	成员运算符
not or and	逻辑运算符

以下实例演示了Python所有运算符优先级的操作：

#!/usr/bin/python

a = 20
b = 10
c = 15
d = 5
e = 0

e = (a + b) * c / d       #( 30 * 15 ) / 5
print "Value of (a + b) * c / d is ",  e

e = ((a + b) * c) / d     # (30 * 15 ) / 5
print "Value of ((a + b) * c) / d is ",  e

e = (a + b) * (c / d);    # (30) * (15/5)
print "Value of (a + b) * (c / d) is ",  e

e = a + (b * c) / d;      #  20 + (150/5)
print "Value of a + (b * c) / d is ",  e

以上实例输出结果：

Value of (a + b) * c / d is 90
Value of ((a + b) * c) / d is 90
Value of (a + b) * (c / d) is 90
Value of a + (b * c) / d is 50