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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 notis 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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