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
== 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。
< 小於 - 回傳x是否小於y。所有比較運算子回傳1表示真,回傳0表示假。這分別與特殊的變數True和False等價。注意,這些變數名的大寫。 (a < b) 回傳 true。
>= 大於等於 - 回傳x是否大於等於y。 (a >= b) 回傳 False。
<= 小於等於 - 回傳x是否小於等於y。 (a <= b) 回傳 true。
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。
<< 左移動運算子 a << 2 輸出結果 240 ,二元解釋: 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/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
>> << 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/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