Python 運算符
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 為10的20次方, 輸出結果 100000000000000000000
//
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
以下假設變量a為10,變量b為20:
運算符
描述
執行個體
==
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.
<>
不等于 - 比較兩個對象是否不相等
(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"
以上執行個體輸出結果:
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指派運算符
以下假設變量a為10,變量b為20:
運算符
描述
執行個體
=
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
以上執行個體輸出結果:
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:
運算符
描述
執行個體
&
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
以上執行個體輸出結果:
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:
運算符
描述
執行個體
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 - Either a is not true or b is not true or both are not true"
else:
print "Line 5 - a and b are true"
以上執行個體輸出結果:
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。
運算符
描述
執行個體
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"
以上執行個體輸出結果:
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身份運算符
身份運算符用于比較兩個對象的存儲單元
運算符
描述
執行個體
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"
以上執行個體輸出結果:
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:
運算符
描述
**
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'
^ |
位運算符
<= < > >=
比較運算符
<> == !=
等于運算符
= %= /= //= -= += *= **=
指派運算符
is is not
身份運算符
in not in
成員運算符
not or and
邏輯運算符
以下執行個體示範了Python所有運算符優先級的操作:
#!/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
以上執行個體輸出結果:
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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