如何解决syntaxerror: more than 255 arguments 报错

问题背景

今天拼接特征的时候，突然代码报错syntaxerror: more than 255 arguments ，看了一下感觉这个报错非常有意思，估计平时也是没机会碰到，和大家分享一下。

解释

SyntaxError: more than 255 arguments 表示你的代码中存在一个语法错误，这个错误通常是因为你在函数调用中传递的参数数量超过了 Python 解释器所允许的上限，该上限为 255【以前确实从来不会给一个函数传200多个参数，但是在实际业务工程中就会碰到这个问题】。

解决方案

可以考虑使用数据结构（例如列表、字典）来重新组织参数，而不是将它们作为独立的参数传递，从而解决该问题。

例如，如果你有一个函数调用如下：

my_function(arg1, arg2, arg3, ..., arg256, arg257)

可以考虑将参数组织成一个列表：

args_list = [arg1, arg2, arg3, ..., arg256, arg257]
my_function(*args_list)

或者字典：

args_dict = {'arg1': val1, 'arg2': val2, ..., 'arg256': val256, 'arg257': val257}
my_function(**args_dict)

但是比较奇怪的是，当我通过dict()包装了我的参数后，仍然报错。也就是说，通过dict()构建一个字典仍然不能超过255个k-v（这也是不被允许的）。于是，我将不同类别特征放入一个字典，然后通过字典的update()函数更新总字典中，这样，而且这样的重构有助于使代码更具可读性，并且可以有序处理大量的参数。如下：

Copy code
args_dict = dict()
args_dict0 = dict('arg1': val1, 'arg2': val2, ..., 'arg254': val254)
args_dict1 = dict('val255': val255, 'arg256': val256, ..., 'arg500': val500)

args_dict.update(args_dict0)
args_dict.update(args_dict1)
my_function(**args_dict)

除此之外，如果参数过多，我们可以通过{} 或者 []构建字典或者list，经过测试是可以一次性构造超过255个元素的。

for i in range(300):
    print("{}:'{}',".format(i,i), end='')
{0:'0',1:'1',2:'2',3:'3',4:'4',5:'5',6:'6',7:'7',8:'8',9:'9',10:'10',11:'11',12:'12',13:'13',14:'14',15:'15',16:'16'
 ,17:'17',18:'18',19:'19',20:'20',21:'21',22:'22',23:'23',24:'24',25:'25',26:'26',27:'27',28:'28',29:'29',30:'30',31:'31',32:'32',33:'33',34:'34',35:'35',36:'36',37:'37',38:'38',39:'39',40:'40',41:'41',42:'42',43:'43',44:'44',45:'45',46:'46',47:'47',48:'48',49:'49',50:'50',51:'51',52:'52',53:'53',54:'54',55:'55',56:'56',57:'57',58:'58',59:'59',60:'60',61:'61',62:'62',63:'63',64:'64',65:'65',66:'66',67:'67',68:'68',69:'69',70:'70',71:'71',72:'72',73:'73',74:'74',75:'75',76:'76',77:'77',78:'78',79:'79',80:'80',81:'81',82:'82',83:'83',84:'84',85:'85',86:'86',87:'87',88:'88',89:'89',90:'90',91:'91',92:'92',93:'93',94:'94',95:'95',96:'96',97:'97',98:'98',99:'99',100:'100',101:'101',102:'102',103:'103',104:'104',105:'105',106:'106',107:'107',108:'108',109:'109',110:'110',111:'111',112:'112',113:'113',114:'114',115:'115',116:'116',117:'117',118:'118',119:'119',120:'120',121:'121',122:'122',123:'123',124:'124',125:'125',126:'126',127:'127',128:'128',129:'129',130:'130',131:'131',132:'132',133:'133',134:'134',135:'135',136:'136',137:'137',138:'138',139:'139',140:'140',141:'141',142:'142',143:'143',144:'144',145:'145',146:'146',147:'147',148:'148',149:'149',150:'150',151:'151',152:'152',153:'153',154:'154',155:'155',156:'156',157:'157',158:'158',159:'159',160:'160',161:'161',162:'162',163:'163',164:'164',165:'165',166:'166',167:'167',168:'168',169:'169',170:'170',171:'171',172:'172',173:'173',174:'174',175:'175',176:'176',177:'177',178:'178',179:'179',180:'180',181:'181',182:'182',183:'183',184:'184',185:'185',186:'186',187:'187',188:'188',189:'189',190:'190',191:'191',192:'192',193:'193',194:'194',195:'195',196:'196',197:'197',198:'198',199:'199',200:'200',201:'201',202:'202',203:'203',204:'204',205:'205',206:'206',207:'207',208:'208',209:'209',210:'210',211:'211',212:'212',213:'213',214:'214',215:'215',216:'216',217:'217',218:'218',219:'219',220:'220',221:'221',222:'222',223:'223',224:'224',225:'225',226:'226',227:'227',228:'228',229:'229',230:'230',231:'231',232:'232',233:'233',234:'234',235:'235',236:'236',237:'237',238:'238',239:'239',240:'240',241:'241',242:'242',243:'243',244:'244',245:'245',246:'246',247:'247',248:'248',249:'249',250:'250',251:'251',252:'252',253:'253',254:'254',255:'255',256:'256',257:'257',258:'258',259:'259',260:'260',261:'261',262:'262',263:'263',264:'264',265:'265',266:'266',267:'267',268:'268',269:'269',270:'270',271:'271',272:'272',273:'273',274:'274',275:'275',276:'276',277:'277',278:'278',279:'279',280:'280',281:'281',282:'282',283:'283',284:'284',285:'285',286:'286',287:'287',288:'288',
 289:'289',290:'290',291:'291',292:'292',293:'293',294:'294',295:'295',296:'296',297:'297',298:'298',299:'299'}

或者

for i in range(300):
    print("{}='{}',".format(i,i), end='')
dict(0='0',1='1',2='2',3='3',4='4',5='5',6='6',7='7',8='8',9='9',10='10',11='11',12='12',13='13',14='14',15='15',
    16='16',17='17',18='18',19='19',20='20',21='21',22='22',23='23',24='24',25='25',26='26',27='27',28='28',29='29',
    30='30',31='31',32='32',33='33',34='34',35='35',36='36',37='37',38='38',39='39',40='40',41='41',42='42',43='43',
    44='44',45='45',46='46',47='47',48='48',49='49',50='50',51='51',52='52',53='53',54='54',55='55',56='56',57='57',
    58='58',59='59',60='60',61='61',62='62',63='63',64='64',65='65',66='66',67='67',68='68',69='69',70='70',71='71',
    72='72',73='73',74='74',75='75',76='76',77='77',78='78',79='79',80='80',81='81',82='82',83='83',84='84',85='85',
    86='86',87='87',88='88',89='89',90='90',91='91',92='92',93='93',94='94',95='95',96='96',97='97',98='98',99='99',
    100='100',101='101',102='102',103='103',104='104',105='105',106='106',107='107',108='108',109='109',110='110',
    111='111',112='112',113='113',114='114',115='115',116='116',117='117',118='118',119='119',120='120',121='121',
    122='122',123='123',124='124',125='125',126='126',127='127',128='128',129='129',130='130',131='131',132='132',
    133='133',134='134',135='135',136='136',137='137',138='138',139='139',140='140',141='141',142='142',143='143',144='144',145='145',146='146',147='147',148='148',149='149',150='150',151='151',152='152',153='153',154='154',155='155',156='156',157='157',158='158',159='159',160='160',161='161',162='162',163='163',164='164',165='165',166='166',167='167',168='168',169='169',170='170',171='171',172='172',173='173',174='174',175='175',176='176',177='177',178='178',179='179',180='180',181='181',182='182',183='183',184='184',185='185',186='186',187='187',188='188',189='189',190='190',191='191',192='192',193='193',194='194',195='195',196='196',197='197',198='198',199='199',200='200',201='201',202='202',203='203',204='204',205='205',206='206',207='207',208='208',209='209',210='210',211='211',212='212',213='213',214='214',215='215',216='216',217='217',218='218',219='219',220='220',221='221',222='222',223='223',224='224',225='225',226='226',227='227',228='228',229='229',230='230',231='231',232='232',233='233',234='234',235='235',236='236',237='237',238='238',239='239',240='240',241='241',242='242',243='243',244='244',245='245',246='246',247='247',248='248',249='249',250='250',251='251',252='252',253='253',254='254',255='255',256='256',257='257',258='258',259='259',260='260',261='261',262='262',263='263',264='264',265='265',266='266',267='267',268='268',269='269',270='270',271='271',272='272',273='273',274='274',275='275',276='276',277='277',278='278',279='279',280='280',281='281',282='282',283='283',284='284',285='285',286='286',287='287',288='288',
    289='289',290='290',291='291',292='292',293='293',294='294',295='295',296='296',297='297',298='298',299='299')