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 输出结果 20

// 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 - a and b are true"
else:
   print "Line 5 - Either a is not true or b is not 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 - a and b are 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