Python学习笔记（五）----Python 运算符

一、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。

      那么，在Python中有哪些类型的运算符呢？

      Python语言支持以下类型的运算符:

1、算术运算符

2、比较（关系）运算符

3、赋值运算符

4、逻辑运算符

5、位运算符

6、成员运算符

7、身份运算符

8、运算符优先级

     下面我们分别对上述的运算符类型进行讲解：

二、Python算术运算符

       为了更好说明这个例子，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yb / 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/pythona = 21b = 10c = 0c = a + bprint "a + b = ", cc = a - bprint "a - b = ", c c = a * bprint "a *b = ", c c = a / bprint "a / b = ", c c = a % bprint "a % b = ", ca = 2b = 3c = a**b print "a ** b = ", ca = 10b = 5c = a//b print "a // b = ", c

以上实例输出结果：

a + b =  31a - b =  11a *b =  210a / b =  2a % b =  1a ** b =  8a // b =  2

三、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/pythona = 21b = 10c = 0if ( 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 bLine 2 - a is not equal to bLine 3 - a is not equal to bLine 4 - a is not less than bLine 5 - a is greater than bLine 6 - a is either less than or equal to  bLine 7 - b is either greater than  or equal to b

四、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/pythona = 21b = 10c = 0c = a + bprint "Line 1 - Value of c is ", cc += aprint "Line 2 - Value of c is ", c c *= aprint "Line 3 - Value of c is ", c c /= a print "Line 4 - Value of c is ", c c  = 2c %= aprint "Line 5 - Value of c is ", cc **= aprint "Line 6 - Value of c is ", cc //= aprint "Line 7 - Value of c is ", c

       以上实例输出结果：

Line 1 - Value of c is  31Line 2 - Value of c is  52Line 3 - Value of c is  1092Line 4 - Value of c is  52Line 5 - Value of c is  2Line 6 - Value of c is  2097152Line 7 - Value of c is  99864

五、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/pythona = 60            # 60 = 0011 1100 b = 13            # 13 = 0000 1101 c = 0c = a & b;        # 12 = 0000 1100print "Line 1 - Value of c is ", cc = a | b;        # 61 = 0011 1101 print "Line 2 - Value of c is ", cc = a ^ b;        # 49 = 0011 0001print "Line 3 - Value of c is ", cc = ~a;           # -61 = 1100 0011print "Line 4 - Value of c is ", cc = a << 2;       # 240 = 1111 0000print "Line 5 - Value of c is ", cc = a >> 2;       # 15 = 0000 1111print "Line 6 - Value of c is ", c

         以上实例输出结果：

Line 1 - Value of c is  12Line 2 - Value of c is  61Line 3 - Value of c is  49Line 4 - Value of c is  -61Line 5 - Value of c is  240Line 6 - Value of c is  15

六、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/pythona = 10b = 20c = 0if ( 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 = 0if ( 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 trueLine 2 - Either a is true or b is true or both are trueLine 3 - Either a is not true or b is not trueLine 4 - Either a is true or b is true or both are trueLine 5 - a and b are true

七、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/pythona = 10b = 20list = [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 = 2if ( 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 listLine 2 - b is not available in the given listLine 3 - a is available in the given list

八、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isis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 1is 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/pythona = 20b = 20if ( 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 = 30if ( 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 identityLine 2 - a and b have same identityLine 3 - a and b do not have same identityLine 4 - a and b do not have same identity

九、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/pythona = 20b = 10c = 15d = 5e = 0e = (a + b) * c / d       #( 30 * 15 ) / 5print "Value of (a + b) * c / d is ",  ee = ((a + b) * c) / d     # (30 * 15 ) / 5print "Value of ((a + b) * c) / d is ",  ee = (a + b) * (c / d);    # (30) * (15/5)print "Value of (a + b) * (c / d) is ",  ee = 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  90Value of ((a + b) * c) / d is  90Value of (a + b) * (c / d) is  90Value of a + (b * c) / d is  50