python 函数支持函数式编程的包operator partial（python安装）

python 函数支持函数式编程的包operator partial（python安装）

itemgetter和attrgetter能替代从序列中取出元素或读取对象属性的lambda表达式，会自动构建函数

itemgetter 1，根据元组某个字段给元组列表排序，下例中

itemgetter(1) == lambda field : field[1]2,如果把多个参数传给itemgetter ,它构建的函数会返回提取的值构成元组

metro_data = [ ("tykyo",'jp',36.944,(35.68944,139.69166)), ("delhi ncr",'in',21.935,(36.64944,138.79166)), ("mexico city",'mx',46.944,(33.68944,129.69166)), ("new york-newark",'us',20.944,(35.68944,139.69166)), ("sao paulo",'br',16.944,(25.68944,149.69166))]#1from operator import itemgetterfor city in sorted(metro_data,key=itemgetter(1)): print(city)#2cc_name=itemgetter(1,0)for city in metro_data: print(cc_name(city))

返回：

('sao paulo', 'br', 16.944, (25.68944, 149.69166))('delhi ncr', 'in', 21.935, (36.64944, 138.79166))('tykyo', 'jp', 36.944, (35.68944, 139.69166))('mexico city', 'mx', 46.944, (33.68944, 129.69166))('new york-newark', 'us', 20.944, (35.68944, 139.69166))-------------------------------------------------------------------------------------('jp', 'tykyo')('in', 'delhi ncr')('mx', 'mexico city')('us', 'new york-newark')('br', 'sao paulo')

attrgetter它创建的函数根据名称提取对象的属性

metro_data = [ ("tykyo",'jp',36.944,(35.68944,139.69166)), ("delhi ncr",'in',21.935,(36.64944,138.79166)), ("mexico city",'mx',46.944,(33.68944,129.69166)), ("new york-newark",'us',20.944,(35.68944,139.69166)), ("sao paulo",'br',16.944,(25.68944,149.69166))]from operator import itemgetterfrom collections import namedtupleLatLong = namedtuple('LatLong','lat long')#定义LatLongMetropolis = namedtuple('Metropolis','name cc pop coord')#定义Metropolis#使用嵌套的元祖拆包提取(Lat,Long)Metro_areas = [Metropolis(name,cc,pop,LatLong(Lat,Long)) for name,cc,pop,(Lat,Long) in metro_data]print(Metro_areas)print(Metro_areas[0])print(Metro_areas[0].coord)print(Metro_areas[0].coord.lat)from operator import attrgettername_lat = attrgetter('name','coord.lat')for city in sorted(Metro_areas,key=attrgetter('coord.lat')): print(name_lat(city))

返回：

[Metropolis(name='tykyo', cc='jp', pop=36.944, coord=LatLong(lat=35.68944, long=139.69166)), Metropolis(name='delhi ncr', cc='in', pop=21.935, coord=LatLong(lat=36.64944, long=138.79166)), Metropolis(name='mexico city', cc='mx', pop=46.944, coord=LatLong(lat=33.68944, long=129.69166)), Metropolis(name='new york-newark', cc='us', pop=20.944, coord=LatLong(lat=35.68944, long=139.69166)), Metropolis(name='sao paulo', cc='br', pop=16.944, coord=LatLong(lat=25.68944, long=149.69166))]Metropolis(name='tykyo', cc='jp', pop=36.944, coord=LatLong(lat=35.68944, long=139.69166))LatLong(lat=35.68944, long=139.69166)35.68944('sao paulo', 25.68944)('mexico city', 33.68944)('tykyo', 35.68944)('new york-newark', 35.68944)('delhi ncr', 36.64944)

functools.partial

:冻结参数

：基于一个函数创建一个新的可调用对象，把原函数的某些参数固定，使用这个函数可以吧接受一个或多个参数的函数改编成需要回调的API，这样参数更少

from operator import mulfrom functools import partialtriple = partial(mul,3)print(triple(7))l = list(map(triple,range(1,10)))print(l)返回：21[3, 6, 9, 12, 15, 18, 21, 24, 27]

def tag(name,*content,cls=None,**attrs): if cls is not None: attrs['class'] = cls if attrs: attrs_str = ''.join(' %s="%s" ' % (attr,value) for attr,value in sorted(attrs.items())) else: attrs_str='' if content: return '\n'.join('<%s %s >%s' % (name,attrs_str,c,name) for c in content) else: return '<%s%s />' % (name,attrs_str)from functools import partialpicture = partial(tag,'img',cls='pic-frame')print(picture)p = picture(src='sunlong.jpeg')print(p)print(picture.args)print(picture.keywords)返回：functools.partial(, 'img', cls='pic-frame')('img',){'cls': 'pic-frame'}

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