# Python 運算符

【摘要】: 本章節主要說明Python的運算符。舉個簡單的例子 4 +5 = 9 。 例子中，4和5被稱為操作數，"+"號為運算符。

什么是運算符？

Python語言支持以下類型的運算符:

## Python算術運算符

+ 加 - 兩個對象相加 a + b 輸出結果 30
- 減 - 得到負數或是一個數減去另一個數 a - b 輸出結果 -10
* 乘 - 兩個數相乘或是返回一個被重復若干次的字符串 a * b 輸出結果 200
/ 除 - x除以y b / a 輸出結果 2
% 取模 - 返回除法的余數 b % a 輸出結果 0
** 冪 - 返回x的y次冪 a**b 為10的20次方， 輸出結果 100000000000000000000
// 取整除 - 返回商的整數部分 9//2 輸出結果 4 , 9.0//2.0 輸出結果 4.0

```#!/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
```

```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比較運算符

== 等于 - 比較對象是否相等 (a == b) 返回 False。
!= 不等于 - 比較兩個對象是否不相等 (a != b) 返回 true.
<> 不等于 - 比較兩個對象是否不相等 (a <> b) 返回 true。這個運算符類似 != 。
> 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。所有比較運算符返回1表示真，返回0表示假。這分別與特殊的變量True和False等價。注意，這些變量名的大寫。 (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。

```#!/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"
```

```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賦值運算符

= 簡單的賦值運算符 c = a + b 將 a + b 的運算結果賦值為 c
+= 加法賦值運算符 c += a 等效于 c = c + a
-= 減法賦值運算符 c -= a 等效于 c = c - a
*= 乘法賦值運算符 c *= a 等效于 c = c * a
/= 除法賦值運算符 c /= a 等效于 c = c / a
%= 取模賦值運算符 c %= a 等效于 c = c % a
**= 冪賦值運算符 c **= a 等效于 c = c ** a
//= 取整除賦值運算符 c //= a 等效于 c = c // a

```#!/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
```

```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位運算符

& 按位與運算符 (a & b) 輸出結果 12 ，二進制解釋： 0000 1100
| 按位或運算符 (a | b) 輸出結果 61 ，二進制解釋： 0011 1101
^ 按位異或運算符 (a ^ b) 輸出結果 49 ，二進制解釋： 0011 0001
~ 按位取反運算符 (~a ) 輸出結果 -61 ，二進制解釋： 1100 0011， 在一個有符號二進制數的補碼形式。
<< 左移動運算符 a << 2 輸出結果 240 ，二進制解釋： 1111 0000
>> 右移動運算符 a >> 2 輸出結果 15 ，二進制解釋： 0000 1111

```#!/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
```

```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邏輯運算符

Python語言支持邏輯運算符，以下假設變量a為10，變量b為20：

and 布爾"與" - 如果x為False，x and y返回False，否則它返回y的計算值。 (a and b) 返回 true。
or 布爾"或" - 如果x是True，它返回True，否則它返回y的計算值。 (a or b) 返回 true。
not 布爾"非" - 如果x為True，返回False。如果x為False，它返回True。 not(a and b) 返回 false。

```#!/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"
```

```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成員運算符

in 如果在指定的序列中找到值返回True，否則返回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沒有找到值返回True，否則返回False。 x 不在 y序列中 , 如果x不在y序列中返回True。

```#!/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"
```

```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身份運算符

is is是判斷兩個標識符是不是引用自一個對象 x is y, 如果 id(x) 等于 id(y) , is 返回結果 1
is not is not是判斷兩個標識符是不是引用自不同對象 x is not y, 如果 id(x) 不等于 id(y). is not 返回結果 1

```#!/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"
```

```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運算符優先級

** 指數 (最高優先級)
~ + - 按位翻轉, 一元加號和減號 (最后兩個的方法名為 [email protected][email protected])
* / % // 乘，除，取模和取整除
+ - 加法減法
>> << 右移，左移運算符
& 位 'AND'
^ | 位運算符
<= < > >= 比較運算符
<> == != 等于運算符
= %= /= //= -= += *= **= 賦值運算符
is is not 身份運算符
in not in 成員運算符
not or and 邏輯運算符

```#!/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
```

```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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