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什么叫魔法函数?

2020年02月14日 移动开发 ⁄ 共 5130字 ⁄ 字号 评论关闭

  什么叫魔法函数(magic method)

607的彩的正确网址  leizhongzhuru__getitem__yishuangxiahuaxiankaishideyixieteshufangfafangfachengweishuangxiafangfa(dunder method),pythonjieshiqiyudaozheixieteshufangfashi,huijihuoyixiejibendeduixiangcaozuo,liru:obj[key]beihoudefangfashi__getitem__,shijibianchengshiyongdeshi:my_collection[key],jieshiqishijidiaoyongdeshimy_collection.__getitem__(key)。leizhongyouhenduozheixieteshufangfa,tamenyeyouyigeteshudenicheng:mofahanshu(magic method).

  zheixieteshufangfaming,nengrangwomendingyideduixiangshixianhezhichihenduoyuyankuangjia,bingyuzhijiaohu,ru:diedai、jihelei、shuxingfangwen、yunsuanfuzhongzai、hanshuhefangfadediaoyong、duixiangdechuangjianhexiaohui、zifuchuanbiaoshixingshihegeshihua、guanlishangxiawen(jiwithkuai)。kenengzheixieyuyankuangjiawomenbuhuidoushuxi,zaihoumiandeneirongzhongyudaole,wozaixiangxijieshao。

  一摞Python风格的纸牌

607的彩的正确网址  womentongguo“yiluopythonfenggedezhipai”yinrulianggemofahanshu:__getitem__、__len__,lejieteshufangfadeqiangda。

  **shilimiaoshu:**zheishiyiluoyouxudezhipai,leimingshezhiweifrenchdeck,yiluopaizhongyou52zhangkapian(card),meiyigekapianyoushiyigelei,yigecardleishezhilianggeshuxing:rank:kapianduiyingdeshuzi,ru:a、1、2、…、j、q、k;suit:kapianduiyingdehuase,ru:spades(heitao)、diamonds(fangkuai)、clubs(meihua)、hearts(hongtao)。

  shejijishu:

  collections.namedtuple chuangjianyigejiandandecardlei (namedtuple:yongyigoujianzhiyoushaoshushuxingdanshimeiyoufangfadeduixiang,birushujukutiaomu)

  random.choice congyigexuliezhongsuijixuanzeyigeyuansu

607的彩的正确网址  neijianhanshusorted() duizhipaigenjuyaoqiujinxingpaixu

  chuangjianlei:

607的彩的正确网址  import collections

607的彩的正确网址  # tongguorandom.choice congyigexuliezhongsuijixuanchuyigeyuansu

  from random import choice

  card = collections.namedtuple('card', ['rank', 'suit']) # chuangjianyigelei,youlianggeshuxingrank、suit

  class frenchdeck:

  # dingyijibenshuxing

  ranks = [str(n) for n in range(2, 11)] + list('jqka') # yifupaizhongdeshuzi

607的彩的正确网址  suits = 'spades diamonds clubs hearts'.split() # yifupaizhongdeyanse

607的彩的正确网址  # dingyisiyoushuxing, shuangxiahuaxian,siyoushuxingzaileiwaibuwufazhijieshiyong,siyoufangfayeshishuangxiahuaxiankaitou, ru: __fun(self)

  __cards = []

607的彩的正确网址  def __init__(self):

607的彩的正确网址  self.__cards = [card(rank, suit) for suit in self.suits for rank in self.ranks] # tongguogouzaohanshuchushihuashuxing

607的彩的正确网址  def __len__(self):

  """

  keyishiyonglen(frenchdeck()) diaoyong

  """

  return len(self.__cards)

  def __getitem__(self, position):

  """

607的彩的正确网址  keyishiyongfrenchdeck()[index] indexweisuoyindefangshihuoquxiangguanshuju,yejiushishuocongyizhuopaizhongchouquyizhangpai

  """

  return self.__cards[position]

  魔法函数使用

  1.tongguolenfangfachakanyiluopaiyouduoshaozhang

  # shilihuagailei

  deck = frenchdeck()

  # chakanyizhuopaipaishu

  print(len(deck))

  2.tongguodeck[index]huoquzheiyizhuopaizhongdiyizhangpai、zuihouyizhangpai

607的彩的正确网址  print(deck[0], deck[-1])

  print(choice(deck))

607的彩的正确网址  3.suijichouquyizhangzhipai

  print(choice(deck))

607的彩的正确网址  4.youyu__getitem__ba[]caozuojiaojileself.__cardsliebiaocaozuo,suoyideckleiyeziranerrandizhichiqiepian(slicing)

607的彩的正确网址  # yiluopaizuishangmian3zhang zhikanpaimianshiadepai

  print(deck[:3])

  print(deck[12::13]) # xianchouchusuoyinshi12deneizhangpai,ranhoumeige13zhangpaiquyizhang

607的彩的正确网址  5.kapaidiedai,jinjinshixian__getitem__jiukeyishizheiyiluopaibianchengkeyidiedaidele。diedaitongchangshiyinshide(yigejiheleixingmeiyoushixian__contains__fangfa),yejiushishuoinyunsuanfujiuhuianshunxuduizhenggejihezuoyicidiedaisousuo

607的彩的正确网址  for card in deck:

  print(card)

  6.fanxiangdiedai,liebiaodenixu

607的彩的正确网址  for card in reversed(deck):

607的彩的正确网址  print(card)

  7.panduanyigeobjectshifouzaizheigejihezhong

  print(card('q', 'hearts') in deck) # chuangjianyigecard('q', 'hearts')lei

607的彩的正确网址  print(card("7", "beasts") in deck)

  8.duizhipaijinxingpaixu,paixuguize:dianshucongxiaodaoda,xiangtongdianshukanhuase,heitao、hongtao、fangkuai、meihuayicijianxiao,jiashemeihua2dedaxiaoshi0, heitiashi51

  suit_values = dict(spades=3, hearts=2, diamonds=1, clubs=0)

  def spades_high(card):

  """

  anzhaoguizejipukepaipaixudehanshu

  """

  rank_value = frenchdeck.ranks.index(card.rank) # huoqudangqianzhipairankdesuoyin

607的彩的正确网址  return rank_value * len(suit_values) + suit_values[card.suit]

607的彩的正确网址  for card in sorted(deck, key=spades_high):

  print(card)

607的彩的正确网址  zaidangqianshejizhongfrenchdeckshibunengxipaide,yinweizheiluopaishibukebiande(immutable),chufeiwomenpohuaizheigeleidefengzhuangxing,gaibian__cardsjinxingcaozuohoumianhuijieshaoruheshiyong__setitem__fangfashixianxipaigongneng。

  如何使用特殊方法

607的彩的正确网址  teshufangfadecunzaishiweilepythonjieshiqidiaoyongde,womenbingbuxuyaodiaoyongtamen,ru:my_object.__len__(),suiranzheiyangxiechengxubuhuibaocuo,womenzuihaohaishishiyonglen(my_object)defangshi。ruguomy_objectshizijichuangjiandelei,zaizhixinglen(my_object)shi,jieshiqihuizijidiaoyongnishixiande__len__fangfa。

  ruguoshiyongdeshineizhideleixing,biruliebiao、zifuchuandeng,neimecpythonduquduiyingneicunzhongzhangdukebiandeneizhiduixiangdecyuyanjiegouti。

  henduoteshufangfadediaoyongshiyinshide,birufor i in x:zheigeyuju,beihouqishiyongdeshiiter(x),erzheigehanshudebeihouzeshix.__iter__()fangfa,qiantishizheigefangfanishixianle。

  tongguoneizhihanshu(ru:len、iter、strdeng)laishiyongteshufangfashizuihaodexuanze。qisudugengkuai。dangranyebuyaosuiyitianjiateshufangfa,ru:__foo__zhileide,suiranzheigeteshufangfaxianzaihaimeiyoubeipythonneibushiyong,danshiyihoujiubuyidingle。

  模拟数值类型

607的彩的正确网址  liyongteshufangfa,keyirangzidingyiduixiangtongguojiahao"+"(huozheqitayunsuanfuhao)jinxingyunsuan。zheijiewomenjieyongyigeerweixiangliang(vector)leilaizhanshiteshufangfadeshiyong。

607的彩的正确网址  zheilidexiangliangjiushioujilidejihezhongchangyongdegainian,zaishuxuehewulizhongjingchangshiyong,ruxiatu,qizhongvector(2,4) + vector(2,1)=vector(4,5),shuoming:suiranpythonneizhidecomplexleikeyiyonglaibiaoshierweixiangliang,danshiwomenzheigezidingyideleikeyikuozhandaonweixiangliang。

  zaishuxievectorleizhiqian,womenxuyaozuochuyixiasikao:

  1.lianggexiangliangxiangjiahouhaishiyigexiangliang,jiyouruxiaxiaoguo

  v1 = vector(2,4)

607的彩的正确网址  v2 = vector(2,1)

  v1 + v2 # vector(4, 5)

607的彩的正确网址  2.neizhihanshuabs,ruguoshurushizhengshuhuozhefudianshu,tafanhuideshishuruzhidejueduizhi,ruguoshurudeshifushu(complex number),fanhuizheigefushudemo,zaishejizheigevectorleishixuyaojiangapiyuqibaochiyizhixing,shuxievectorleishixuyaoduiabshanshuzuoxiangguanchuli,jizaipengdaoabshanshushi,yeyinggaifanhuigaixiangliangdemo,jiyouruxiaxiaoguo

607的彩的正确网址  v = vector(3, 4)

  print(abs(v)) # 5.0

  3.liyong*yunsuanfulaishixianxiangliangdebiaoliangchengfa(xiangliangyushudechengfa,dedaodejieguoxiangliangyuyuanxiangliangbaochiyizhi,mobianda),jiyouruxiaxiaoguo

607的彩的正确网址  v * 3 # vector(9,12)

607的彩的正确网址  abs(v*3) # 15.0

  shejizhishi:

  math.hypot math.hypot(x, y) fanhuioujilidefanshu sqrt(x*x + y*y)

  womenzanshixiankaolvzheimeduo,xianshixianyigejiandandexiangliang,qizhongshiyongle:__repr__、__abs__、__add__、__mul__。

  from math import hypot

607的彩的正确网址  class vector:

  # vectorgouzaohanshu

  def __init__(self, x=0, y=0):

607的彩的正确网址  self.x = x

  self.y = y

607的彩的正确网址  # 1 yizifuchuanxingshidayinxiangliang,fouzedayin:leixing、dizhidengxinxi

  def __repr__(self):

  return 'vector(%r, %r)' % (self.x, self.y)

  # return 'vector({}, {})'.format(self.x, self.y)

  # shixianxiangliangabsqumo

607的彩的正确网址  def __abs__(self):

  return hypot(self.x, self.y)

  # shixianxiangliangxiangjia

  def __add__(self, other):

607的彩的正确网址  x = self.x + other.x

607的彩的正确网址  y = self.y + other.y

  return vector(x, y)

607的彩的正确网址  # shixianxiangliangchengyiyigebiaoliang

  def __mul__(self, scalar):

607的彩的正确网址  return vector(self.x * scalar, self.y * scalar)

  **shuoming:**zaishiyongxiangliangyubiaoliangxiangchengdeshihou,biaoliangzhinengzaixianglianghou。yejiushishuohulvelechengfadejiaohuanlv,zaihoumianhuijinyibujieshaoshiyong__rmul__laijiejuezheigewenti。

  字符串表示形式

607的彩的正确网址  pythonyouyigeneizhihanshurepr,tanengbayigeduixiangyongzifuchuandexingshibiaodachulaiyibianbianren,zheijiushi”zifuchuanbiaoshixingshi“。reprjiushitongguo__repr__zheigeteshufangfalaidedaoyigeduixiangdezifuchuanxingshi,ruguomeiyoushixian__repr__,neimedayinduixiangshi,dedaodezifuchuankenengyouruxiaxingshi:,zifuchuanfanhuiyekeyishiyongstr.format()jinxingzifuxiugai。

  zai__repr__shixianzhong,tongguo%rhuo{}zhanwei,jiuanshivector(1, 2) yu vector('1’, '2’)shibuyiyangde,zheibaozhengleshujuleixingdewending,yinweixiangliangdegouzaohanshuzhijieshoushuzhi,bujieshouzifuchuan。

  __repr__yu__str__juyouxiangtongdegongneng,danshiyunxingzhonghaishiyouqubiede,houzheshizaistr()hanshubeishiyongshi,huoshizaiyongprinthanshudayinyigeduixiangdeshihoucaibeidiaoyong,tafanhuidezifuchuanduizhongduanyonghugengyouhao。danzhixiangshixianlianggeteshufangfazhongdeyige,__repre__shigenghaodexuanze,yinweiruguoyigeduixiangmeiyou__str__hanshu,erpythonyouxuyaodiaoyongtadeshihou,jieshiqihuiyong__repr__zuoweitidai。

  算数运算符

  tongguo__add__、__mul__zaishanglizhongshixianle+ he* zheilianggeyunsuanfu。zheilianggefangfadefanhuizhidoushixinchuangjiandexiangliangduixiang,beicaozuodelianggexiangliangyuanfengweidong,daimazhiduquleqiduiyingdeshuzhi,zheijiushizhongzhuiyunsuanfudejibenyuanze。

  自定义的布尔值

  jinguanpythonliyouboolleixing,danshijishangrenheduixiangdoukeyiyongyuxuyaobuerzhideshangxiawenzhong(ru:if 、while、and、or、notyunsuanfu)。weilepanduanyigezhixweizhenhaishijia,pythonhuidiaoyongbool(x),zheigehanshuzhinengfanhuitruehuofalse。

  morenqingkuangxia,womenzijidingyideleideshilizongbeirenweishizhende,chufeizheigeleidui__bool__huozhe__len__hanshuyouzijideshixian。bool(x)debeihoushidiaoyongx.__bool__()dejieguo,ruguobucunzai__bool__fangfa,neimebool(x)huichangshidiaoyongx.__len__()。ruofanhui0,zeboolhuifanhuifalse,fouzefanhuitrue。

607的彩的正确网址  dui__bool__deshixianhenjiandan,ruguoyigexiangliangdemoshi0,neimejiufanhuiyigefalse,qitaqingkuangfanhuitrue。yinwei__bool__hanshudefanhuileixingyinggaishibuerxing,suoyiwomentongguobool(abs(self))bamozhibianchengbuerzhi。(return bool(self.x or self.y)huigengkuai。

baoqian!pinglunyiguanbi.

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