• Python

• # 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:

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 [email protected][email protected])
* / % // 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
``` 2
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