operator模块是python中内置的操作符函数接口,它定义了一些算术和比较内置操作的函数。operator模块是用c实现的,所以执行速度比python代码快。
逻辑操作
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from operator import *
a = [ 1 , 2 , 3 ]
b = a
print 'a =' , a
print 'b =' , b
print
print 'not_(a) :' , not_(a)
print 'truth(a) :' , truth(a)
print 'is_(a, b) :' , is_(a, b)
print 'is_not(a, b) :' , is_not(a, b)
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打印结果:
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a = [1, 2, 3]
b = [1, 2, 3]
not_(a) : False
truth(a) : True
is_(a, b) : True
is_not(a, b): False
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可以通过结果知道,operator的一些操作函数与原本的运算是相同的。
比较操作符
operator提供丰富的比较操作。
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a = 3
b = 5
print 'a =' , a
print 'b =' , b
print
for func in (lt, le, eq, ne, ge, gt):
print '{0}(a, b):' . format (func.__name__), func(a, b)
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打印结果
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a = 3
b = 5
lt(a, b): True
le(a, b): True
eq(a, b): False
ne(a, b): True
ge(a, b): False
gt(a, b): False
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这些函数等价于<、<=、==、>=和>的表达式语法。
算术操作符
处理数字的算术操作符也得到支持。
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a, b, c, d = - 1 , 2 , - 3 , 4
print 'a =' , a
print 'b =' , b
print 'c =' , c
print 'd =' , d
print '\nPositive/Negative:'
print 'abs(a):' , abs (a)
print 'neg(a):' , neg(a)
print 'neg(b):' , neg(b)
print 'pos(a):' , pos(a)
print 'pos(b):' , pos(b)
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打印结果
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a = -1
b = 2
c = -3
d = 4
Positive/Negative:
abs(a): 1
neg(a): 1
neg(b): -2
pos(a): -1
pos(b): 2
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abs返回值得绝对值,neg返回(-obj), pos返回(+obj)。
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a = - 2
b = 5.0
print 'a =' , a
print 'b =' , b
print '\nArithmetic'
print 'add(a, b) :' , add(a, b)
print 'div(a, b) :' , div(a, b)
print 'floordiv(a, b) :' , floordiv(a, b)
print 'mod(a, b) :' , mod(a, b)
print 'mul(a, b) :' , mul(a, b)
print 'pow(a, b) :' , pow (a, b)
print 'sub(a, b) :' , sub(a, b)
print 'truediv(a, b) :' , truediv(a, b)
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打印结果
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a = -2
b = 5.0
Arithmetic
add(a, b) : 3.0
div(a, b) : -0.4
floordiv(a, b) : -1.0
mod(a, b) : 3.0 # 查看负数取模
mul(a, b) : -10.0
pow(a, b) : -32.0
sub(a, b) : -7.0
truediv(a, b) : -0.4
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mod表示取模, mul 表示相乘,pow是次方, sub表示相减
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a = 2
b = 6
print 'a =' , a
print 'b =' , b
print '\nBitwise:'
print 'and_(a, b) :' , and_(a, b)
print 'invert(a) :' , invert(a)
print 'lshift(a, b) :' , lshift(a, b)
print 'or_(a, b) :' , or_(a, b)
print 'rshift(a, b) :' , rshift(a, b)
print 'xor(a, b) :' , xor(a, b)
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打印结果
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a = 2
b = 6
Bitwise:
and_(a, b) : 2
invert(a) : -3
lshift(a, b) : 128
or_(a, b) : 6
rshift(a, b) : 0
xor(a, b) : 4
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and 表示按位与, invert 表示取反操作, lshift表示左位移, or表示按位或, rshift表示右位移,xor表示按位异或。
原地操作符
即in-place操作, x += y 等同于 x = iadd(x, y), 如果复制给其他变量比如z = iadd(x, y)等同与z = x; z += y。
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a = 3
b = 4
c = [ 1 , 2 ]
d = [ 'a' , 'b' ]
print 'a =' , a
print 'b =' , b
print 'c =' , c
print 'd =' , d
print
a = iadd(a, b)
print 'a = iadd(a, b) =>' , a
print
c = iconcat(c, d)
print 'c = iconcat(c, d) =>' , c
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属性和元素的获取方法
operator模块最特别的特性之一就是获取方法的概念,获取方法是运行时构造的一些可回调对象,用来获取对象的属性或序列的内容,获取方法在处理迭代器或生成器序列的时候特别有用,它们引入的开销会大大降低lambda或Python函数的开销。
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from operator import *
class MyObj( object ):
def __init__( self , arg):
super (MyObj, self ).__init__()
self .arg = arg
def __repr__( self ):
return 'MyObj(%s)' % self .arg
objs = [MyObj(i) for i in xrange ( 5 )]
print "Object:" , objs
g = attrgetter( "arg" )
vals = [g(i) for i in objs]
print "arg values:" , vals
objs.reverse()
print "reversed:" , objs
print "sorted:" , sorted (objs, key = g)
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结果:
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Object: [MyObj(0), MyObj(1), MyObj(2), MyObj(3), MyObj(4)]
arg values: [0, 1, 2, 3, 4]
reversed: [MyObj(4), MyObj(3), MyObj(2), MyObj(1), MyObj(0)]
sorted: [MyObj(0), MyObj(1), MyObj(2), MyObj(3), MyObj(4)]
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属性获取方法类似于
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lambda x, n = 'attrname' : getattr (x,nz)
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元素获取方法类似于
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lambda x,y = 5 :x[y]
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from operator import *
l = [ dict (val = - 1 * i) for i in xrange ( 4 )]
print "dictionaries:" , l
g = itemgetter( "val" )
vals = [g(i) for i in l]
print "values: " , vals
print "sorted:" , sorted (l, key = g)
l = [(i,i * - 2 ) for i in xrange ( 4 )]
print "tuples: " , l
g = itemgetter( 1 )
vals = [g(i) for i in l]
print "values:" , vals
print "sorted:" , sorted (l, key = g)
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结果如下:
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dictionaries: [{'val': 0}, {'val': -1}, {'val': -2}, {'val': -3}]
values: [0, -1, -2, -3]
sorted: [{'val': -3}, {'val': -2}, {'val': -1}, {'val': 0}]
tuples: [(0, 0), (1, -2), (2, -4), (3, -6)]
values: [0, -2, -4, -6]
sorted: [(3, -6), (2, -4), (1, -2), (0, 0)]
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除了序列之外,元素获取方法还适用于映射。
结合操作符和定制类
operator模块中的函数通过相应操作的标准Python接口完成工作,所以它们不仅适用于内置类型,还适用于用户自定义类型。
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from operator import *
class MyObj( object ):
def __init__( self , val):
super (MyObj, self ).__init__()
self .val = val
return
def __str__( self ):
return "MyObj(%s)" % self .val
def __lt__( self , other):
return self .val < other.val
def __add__( self , other):
return MyObj( self .val + other.val)
a = MyObj( 1 )
b = MyObj( 2 )
print lt(a, b)
print add(a,b)
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结果如下所示:
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True
MyObj(3)
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类型检查
operator 模块还包含一些函数用来测试映射、数字和序列类型的API兼容性。
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from operator import *
class NoType( object ):
pass
class MultiType( object ):
def __len__( self ):
return 0
def __getitem__( self , name):
return "mapping"
def __int__( self ):
return 0
o = NoType()
t = MultiType()
for func in [isMappingType, isNumberType, isSequenceType]:
print "%s(o):" % func.__name__, func(o)
print "%s(t):" % func.__name__, func(t)
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结果如下:
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isMappingType(o): False
isMappingType(t): True
isNumberType(o): False
isNumberType(t): True
isSequenceType(o): False
isSequenceType(t): True
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但是这些测试并不完善,因为借口没有严格定义。
获取对象方法
使用methodcaller可以获取对象的方法。
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from operator import methodcaller
class Student( object ):
def __init__( self , name):
self .name = name
def getName( self ):
return self .name
stu = Student( "Jim" )
func = methodcaller( 'getName' )
print func(stu) # 输出Jim
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还可以给方法传递参数:
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f = methodcaller( 'name' , 'foo' , bar = 1 )
f(b) # return b.name('foo', bar=1)
methodcaller方法等价于下面这个函数:
def methodcaller(name, * args, * * kwargs):
def caller(obj):
return getattr (obj, name)( * args, * * kwargs)
return caller
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