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
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