什麼是運算符？
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，"+"号為運算符。
Python語言支援以下類型的運算符:
- 算術運算符
- 比較（關系）運算符
- 指派運算符
- 邏輯運算符
- 位運算符
- 成員運算符
- 身份運算符
- 運算符優先級
接下來讓我們一個個來學習Python的運算符。
Python算術運算符
以下假設變量a為10，變量b為20：
| 運算符 | 描述 | 執行個體 |
|---|---|---|
| + | 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 - 兩個數相乘或是傳回一個被重複若幹次的字元串 | a * b 輸出結果 200 |
| / | 除 - x除以y | b / a 輸出結果 2 |
| % | 取模 - 傳回除法的餘數 | b % a 輸出結果 0 |
| ** | 幂 - 傳回x的y次幂 | a**b 輸出結果 20 |
| // | 取整除 - 傳回商的整數部分 | 9//2 輸出結果 4 , 9.0//2.0 輸出結果 4.0 |
以下執行個體示範了Python所有算術運算符的操作：
#!/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 以上執行個體輸出結果：
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比較運算符
| == | 等于 - 比較對象是否相等 | (a == b) 傳回 False。 |
| != | 不等于 - 比較兩個對象是否不相等 | (a != b) 傳回 true. |
| <> | (a <> b) 傳回 true。這個運算符類似 != 。 | |
| > | 大于 - 傳回x是否大于y | (a > b) 傳回 False。 |
| < | 小于 - 傳回x是否小于y。所有比較運算符傳回1表示真，傳回0表示假。這分别與特殊的變量True和False等價。注意，這些變量名的大寫。 | (a < b) 傳回 true。 |
| >= | 大于等于 - 傳回x是否大于等于y。 | (a >= b) 傳回 False。 |
| <= | 小于等于 - 傳回x是否小于等于y。 | (a <= b) 傳回 true。 |
以下執行個體示範了Python所有比較運算符的操作：
#!/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" 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指派運算符
| = | 簡單的指派運算符 | c = a + b 将 a + b 的運算結果指派為 c |
| += | 加法指派運算符 | c += a 等效于 c = c + a |
| -= | 減法指派運算符 | c -= a 等效于 c = c - a |
| *= | 乘法指派運算符 | c *= a 等效于 c = c * a |
| /= | 除法指派運算符 | c /= a 等效于 c = c / a |
| %= | 取模指派運算符 | c %= a 等效于 c = c % a |
| **= | 幂指派運算符 | c **= a 等效于 c = c ** a |
| //= | 取整除指派運算符 | c //= a 等效于 c = c // a |
以下執行個體示範了Python所有指派運算符的操作：
#!/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 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
按位運算符是把數字看作二進制來進行計算的。Python中的按位運算法則如下：
| & | 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， 在一個有符号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 |
以下執行個體示範了Python所有位運算符的操作：
#!/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 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語言支援邏輯運算符，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傳回False，否則它傳回y的計算值。 | (a and b) 傳回 true。 |
| or | 布爾"或" - 如果x是True，它傳回True，否則它傳回y的計算值。 | (a or b) 傳回 true。 |
| not | 布爾"非" - 如果x為True，傳回False。如果x為False，它傳回True。 | not(a and b) 傳回 false。 |
以下執行個體示範了Python所有邏輯運算符的操作：
#!/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" 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成員運算符
除了以上的一些運算符之外，Python還支援成員運算符，測試執行個體中包含了一系列的成員，包括字元串，清單或元組。
| in | 如果在指定的序列中找到值傳回True，否則傳回False。 | x 在 y序列中 , 如果x在y序列中傳回True。 |
| not in | 如果在指定的序列中沒有找到值傳回True，否則傳回False。 | x 不在 y序列中 , 如果x不在y序列中傳回True。 |
以下執行個體示範了Python所有成員運算符的操作：
#!/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" 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
身份運算符用于比較兩個對象的存儲單元
| is | is是判斷兩個辨別符是不是引用自一個對象 | x is y, 如果 id(x) 等于 id(y) , is 傳回結果 1 |
| is not | is not是判斷兩個辨別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 傳回結果 1 |
以下執行個體示範了Python所有身份運算符的操作：
#!/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" 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
以下表格列出了從最高到最低優先級的所有運算符：
| 指數 (最高優先級) | |
| ~ + - | 按位翻轉, 一進制加号和減号 (最後兩個的方法名為 +@ 和 -@) |
| * / % // | 乘，除，取模和取整除 |
| + - | 加法減法 |
| >> << | 右移，左移運算符 |
| 位 'AND' | |
| ^ | | |
| <= < > >= | 比較運算符 |
| <> == != | 等于運算符 |
| = %= /= //= -= += *= **= | |
| is is not | |
| in not in | |
| not or and |
#!/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