Python 運算符

什麼是運算符？

本章節主要說明Python的運算子。舉個簡單的例子 4 +5 = 9 。 範例中，4和5稱為操作數，"+"號為運算子。

Python語言支援以下類型的運算子:

算術運算子

比較（關係）運算子

賦值運算子

邏輯運算子

算運算子

運算子優先權

接下來讓我們一個個來學習Python的運算子。

Python算術運算子

以下假設變數a為10，變數b為20：

運算子

描述

-    減- 得到負數或是一個數減去另一個數   a - b 輸出結果-10    

*    乘- 兩個數相乘或是將一個被重複為若干次的字串  a b 

/    除- x除以y    b / a 輸出結果2    

%    取模- 返回除法的餘數   b % a 輸出結果0   取模- 返回除法的餘數   b % a 輸出結果0   取模- 返回除法的餘數   b % a 輸出結果 0  

//    取整除- 返回商數的整數部分   9//2 輸出結果4 , 9.0//2.0 輸出結果4.0    

以下實例示範了Python所有算術運算子的運算範例輸出結果：

#!/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

   

Python比較運算子

下列假設變數a為10，變數b為20：實例說明實例

==    等於-比較物件是否相等   (a == b) 回傳False。    

!=    不等於 - 比較兩個物件是否相等    (a != b) 回傳 true.    

   不等於 - 比較兩個物件是否相等 true這個運算子類似 != 。    

>    大於 - 回傳x是否大於y    (a > b) 回傳 False。    

>=    大於等於 - 回傳x是否大於等於y。    (a >= b) 回傳 False。    

以下實例示範了Python所有比較運算子的運算：

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賦值運算子

實例

=    簡單的賦值運算子   c = a + b 將a + b 的運算結果賦值為c    

+=  值加法賦值

-=    減法賦值運算子   c -= a 等效於c = c - a    

*=     賦值運算子   c *= a 等效於 等效於c = c / a    

%=    取模賦值運算子   c %= a 等效於c = c % a    

**=   我賦值運算子* a    

//=    取整除賦值運算符   c //= a 等效於c = c // a    

以下實例演示了Python所有賦值運算符的操作：

#!/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位元運算子

位元運算子是把數字看作二進位來進行計算的。 Python中的位元運演算法則如下：

運算子

描述

實例

&       按位或運算子   (a | b) 輸出結果61 ，二進位解釋： 0011 1101    

^    按位異或運算子   (a ^ b) 輸出結果49 ，二進位解釋：00011 符   ( ~a ) 輸出結果-61 ，二進位解釋： 1100 0011， 在一個有符號二進位數的補碼形式。    

>>    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 - 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 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 - a and b are 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    

>> 576f6c06acde14831fa5e2d2bcea0818 >=    比较运算符    

a8093152e673feb7aba1828c43532094 == !=    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

a + (b * c) / d 的值為 50