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

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