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本章节主要说明Python的运算符。举个简单的例子 4 +5 = 9 。 例子中,4和5被称为操作数,"+"号为运算符。 Python语言支持以下类型的运算符: * [算术运算符](http://www.runoob.com/python/python-operators.html#ysf1) * [比较(关系)运算符](http://www.runoob.com/python/python-operators.html#ysf2) * [赋值运算符](http://www.runoob.com/python/python-operators.html#ysf3) * [逻辑运算符](http://www.runoob.com/python/python-operators.html#ysf4) * [位运算符](http://www.runoob.com/python/python-operators.html#ysf5) * [成员运算符](http://www.runoob.com/python/python-operators.html#ysf6) * [身份运算符](http://www.runoob.com/python/python-operators.html#ysf7) * [运算符优先级](http://www.runoob.com/python/python-operators.html#ysf8) 接下来让我们一个个来学习Python的运算符。 ## Python算术运算符 以下假设变量a为10,变量b为20: | 运算符 | 描述 | 实例 | |--|--|--| | + | 加 - 两个对象相加 | a + b 输出结果 30 | | - | 减 - 得到负数或是一个数减去另一个数 | a - b 输出结果 -10 | | * | 乘 - 两个数相乘或是返回一个被重复若干次的字符串 | a * b 输出结果 200 | | / | 除 - x除以y | b / a 输出结果 2 | | % | 取模 - 返回除法的余数 | b % a 输出结果 0 | | ** | 幂 - 返回x的y次幂 | a**b 为10的20次方, 输出结果 100000000000000000000 | | // | 取整除 - 返回商的整数部分 | 9//2 输出结果 4 , 9.0//2.0 输出结果 4.0 | 以下实例演示了Python所有算术运算符的操作: ~~~ #!/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 ~~~ [](http://www.runoob.com/try/showpy.php?filename=test_operator&language=py)尝试一下 » 以上实例输出结果: ~~~ 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比较运算符 以下假设变量a为10,变量b为20: | 运算符 | 描述 | 实例 | |--|--|--| | == | 等于 - 比较对象是否相等 | (a == b) 返回 False。 | | != | 不等于 - 比较两个对象是否不相等 | (a != b) 返回 true. | | | 不等于 - 比较两个对象是否不相等 | (a | | > | 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。所有比较运算符返回1表示真,返回0表示假。这分别与特殊的变量True和False等价。注意,这些变量名的大写。 | (a | | >= | 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 | 以下实例演示了Python所有比较运算符的操作: ~~~ #!/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赋值运算符 以下假设变量a为10,变量b为20: | 运算符 | 描述 | 实例 | |--|--|--| | = | 简单的赋值运算符 | c = a + b 将 a + b 的运算结果赋值为 c | | += | 加法赋值运算符 | c += a 等效于 c = c + a | | -= | 减法赋值运算符 | c -= a 等效于 c = c - a | | *= | 乘法赋值运算符 | c *= a 等效于 c = c * a | | /= | 除法赋值运算符 | c /= a 等效于 c = c / a | | %= | 取模赋值运算符 | c %= a 等效于 c = c % a | | **= | 幂赋值运算符 | c **= a 等效于 c = c ** a | | //= | 取整除赋值运算符 | c //= a 等效于 c = c // a | 以下实例演示了Python所有赋值运算符的操作: ~~~ #!/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 ~~~ 以上实例输出结果: ~~~ 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位运算符 按位运算符是把数字看作二进制来进行计算的。Python中的按位运算法则如下: | 运算符 | 描述 | 实例 | |--|--|--| | & | 按位与运算符 | (a & b) 输出结果 12 ,二进制解释: 0000 1100 | | 按位或运算符 | (a | b) 输出结果 61 ,二进制解释: 0011 1101 | | ^ | 按位异或运算符 | (a ^ b) 输出结果 49 ,二进制解释: 0011 0001 | | ~ | 按位取反运算符 | (~a ) 输出结果 -61 ,二进制解释: 1100 0011, 在一个有符号二进制数的补码形式。 | | | 左移动运算符 | a | | >> | 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 - 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 - Either a is not true or b is not true or both are not 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 Value of a + (b * c) / d is 50 ~~~