google的python编码规范Word文件下载.docx

google的python编码规范Word文件下载.docx

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True/Falseevaluations 

DeprecatedLanguageFeaturesLexicalScoping 

FunctionandMethodDecorators 

Threading 

PowerFeatures

PythonStyleRules

Semicolons 

Linelength 

Parentheses 

Indentation 

BlankLines 

Whitespace 

PythonInterpreterComments 

Classes 

Strings 

TODOComments 

Importsformatting 

Statements 

AccessControl 

NamingMain

ImportantNote

DisplayingHiddenDetailsinthisGuide

link▽

Thisstyleguidecontainsmanydetailsthatareinitiallyhiddenfromview.Theyaremarkedbythetriangleicon,whichyouseehereonyourleft.Clickitnow.Youshouldsee"

Hooray"

appearbelow.

Hooray!

Nowyouknowyoucanexpandpointstogetmoredetails.Alternatively,there'

sa"

toggleall"

atthetopofthisdocument.

Background

PythonisthemainscriptinglanguageusedatGoogle.Thisstyleguideisalistof 

dosand 

don'

tsforPythonprograms.

Tohelpyouformatcodecorrectly,we'

vecreateda 

settingsfileforVim.ForEmacs,thedefaultsettingsshouldbefine.

pychecker

Run 

overyourcode.

Definition:

PyCheckerisatoolforfindingbugsinPythonsourcecode.ItfindsproblemsthataretypicallycaughtbyacompilerforlessdynamiclanguageslikeCandC++.Itissimilartolint.BecauseofthedynamicnatureofPython,somewarningsmaybeincorrect;

however,spuriouswarningsshouldbefairlyinfrequent.

Pros:

Catcheseasy-to-misserrorsliketypos,use-vars-before-assignment,etc.

Cons:

isn'

tperfect.Totakeadvantageofit,we'

llneedtosometimes:

a）Writearounditb）Suppressitswarningsc）Improveitord）Ignoreit.

Decision:

Makesureyourun 

onyourcode.

Forinformationonhowtorun 

pychecker,seethe 

pycheckerhomepage

Tosuppresswarnings,youcansetamodule-levelvariablenamed 

__pychecker__ 

tosuppressappropriatewarnings.Forexample:

__pychecker__='

no-callinitno-classattr'

Suppressinginthiswayhastheadvantagethatwecaneasilysearchforsuppressionsandrevisitthem.

Youcangetalistofpycheckerwarningsbydoing 

pychecker--help.

Unusedargumentwarningscanbesuppressedbyusing`_'

astheidentifierfortheunusedargumentorprefixingtheargumentnamewith`unused_'

.Insituationswherechangingtheargumentnamesisinfeasible,youcanmentionthematthebeginningofthefunction.Forexample:

deffoo（a,unused_b,unused_c,d=None,e=None）:

（d,e）=（d,e）#Silencepychecker

returna

Ideally,pycheckerwouldbeextendedtoensurethatsuch`unuseddeclarations'

weretrue.

Imports

Use 

importsforpackagesandmodulesonly.

Reusabilitymechanismforsharingcodefromonemoduletoanother.

Thenamespacemanagementconventionissimple.Thesourceofeachidentifierisindicatedinaconsistentway;

x.Obj 

saysthatobject 

Obj 

isdefinedinmodule 

x.

Modulenamescanstillcollide.Somemodulenamesareinconvenientlylong.

importx 

forimportingpackagesandmodules. 

fromximporty 

where 

x 

isthepackageprefixand 

y 

isthemodulenamewithnoprefix. 

fromximportyasz 

iftwomodulesnamed 

z 

aretobeimportedorif 

isaninconvenientlylongname.

Forexamplethemodule 

sound.effects.echo 

maybeimportedasfollows:

fromsound.effectsimportecho

...

echo.EchoFilter（input,output,delay=0.7,atten=4）

Donotuserelativenamesinimports.Evenifthemoduleisinthesamepackage,usethefullpackagename.Thishelpspreventunintentionallyimportingapackagetwice.

Packages

Importeachmoduleusingthefullpathnamelocationofthemodule.

Avoidsconflictsinmodulenames.Makesiteasiertofindmodules.

Makesithardertodeploycodebecauseyouhavetoreplicatethepackagehierarchy.

Allnewcodeshouldimporteachmodulebyitsfullpackagename.

Importsshouldbeasfollows:

#Referenceincodewithcompletename.

importsound.effects.echo

#Referenceincodewithjustmodulename（preferred）.

Exceptions

Exceptionsareallowedbutmustbeusedcarefully.

Exceptionsareameansofbreakingoutofthenormalflowofcontrolofacodeblocktohandleerrorsorotherexceptionalconditions.

Thecontrolflowofnormaloperationcodeisnotclutteredbyerror-handlingcode.Italsoallowsthecontrolflowtoskipmultipleframeswhenacertainconditionoccurs,e.g.,returningfromNnestedfunctionsinonestepinsteadofhavingtocarry-througherrorcodes.

Maycausethecontrolflowtobeconfusing.Easytomisserrorcaseswhenmakinglibrarycalls.

Exceptionsmustfollowcertainconditions:

∙Raiseexceptionslikethis:

raiseMyException（"

Errormessage"

） 

or 

raiseMyException.Donotusethetwo-argumentform（raiseMyException,"

）ordeprecatedstring-basedexceptions（raise"

）.

∙Modulesorpackagesshoulddefinetheirowndomain-specificbaseexceptionclass,whichshouldinheritfromthebuilt-inExceptionclass.Thebaseexceptionforamoduleshouldbecalled 

Error.

∙classError（Exception）:

pass

∙Neverusecatch-all 

except:

statements,orcatch 

Exception 

StandardError,unlessyouarere-raisingtheexceptionorintheoutermostblockinyourthread（andprintinganerrormessage）.Pythonisverytolerantinthisregardandexcept:

willreallycatcheverythingincludingPythonsyntaxerrors.Itiseasytohiderealbugsusing 

.

∙Minimizetheamountofcodeina 

try/except 

block.Thelargerthebodyofthe 

try,themorelikelythatanexceptionwillberaisedbyalineofcodethatyoudidn'

texpecttoraiseanexception.Inthosecases,the 

blockhidesarealerror.

∙Usethe 

finally 

clausetoexecutecodewhetherornotanexceptionisraisedinthe 

try 

block.Thisisoftenusefulforcleanup,i.e.,closingafile.

Globalvariables

Avoidglobalvariables.

Variablesthataredeclaredatthemodulelevel.

Occasionallyuseful.

Hasthepotentialtochangemodulebehaviorduringtheimport,becauseassignmentstomodule-levelvariablesaredonewhenthemoduleisimported.

Avoidglobalvariablesinfavorofclassvariables.Someexceptionsare:

∙Defaultoptionsforscripts.

∙Module-levelconstants.Forexample:

PI=3.14159.Constantsshouldbenamedusingallcapswithunderscores;

seeNaming 

below.

∙Itissometimesusefulforglobalstocachevaluesneededorreturnedbyfunctions.

∙Ifneeded,globalsshouldbemadeinternaltothemoduleandaccessedthroughpublicmodulelevelfunctions;

see 

Namingbelow.

Nested/Local/InnerClassesandFunctions

Nested/local/innerclassesandfunctionsarefine.

Aclasscanbedefinedinsideofamethod,function,orclass.Afunctioncanbedefinedinsideamethodorfunction.Nestedfunctionshaveread-onlyaccesstovariablesdefinedinenclosingscopes.

Allowsdefinitionofutilityclassesandfunctionsthatareonlyusedinsideofaverylimitedscope.Very 

ADT-y.

Instancesofnestedorlocalclassescannotbepickled.

Theyarefine.

ListComprehensions

Okaytouseforsimplecases.

Listcomprehensionsandgeneratorexpressionsprovideaconciseandefficientwaytocreatelistsanditeratorswithoutresortingtotheuseof 

map（）, 

filter（）,or 

lambda.

Simplelistcomprehensionscanbeclearerandsimplerthanotherlistcreationtechniques.Generatorexpressionscanbeveryefficient,sincetheyavoidthecreationofalistentirely.

Complicatedlistcomprehensionsorgeneratorexpressionscanbehardtoread.

Okaytouseforsimplecases.Eachportionmustfitononeline:

mappingexpression, 

for 

clause,filterexpression.Multiplefor 

clausesorfilterexpressionsarenotpermitted.Useloopsinsteadwhenthingsgetmorecomplicated.

No:

result=[（x,y）forxinrange（10）foryinrange（5）ifx*y>

10]

return（（x,y,z）

forxinxrange（5）

foryinxrange（5）

ifx!

=y

forzinxrange（5）

ify!

=z）

Yes:

result=[]

forxinrange（10）:

foryinrange（5）:

ifx*y>

10:

result.append（（x,y））

forxinxrange（5）:

foryinxrange（5）:

=y:

forzinxrange（5）:

=z:

yield（x,y,z）

return（（x,complicated_transform（x））

forxinlong_generator_function（parameter）

ifxisnotNone）

squares=[x*xforxinrange（10）]

eat（jelly_beanforjelly_beaninjelly_beans

ifjelly_bean.color=='

black'

）

DefaultIteratorsandOperators

Usedefaultiteratorsandoperatorsfortypesthatsupportthem,likelists,dictionaries,andfiles.

Containertypes,likedictionariesandlists,definedefaultiteratorsandmembershiptestoperators（"

in"

and"

notin"

Thedefaultiteratorsandoperatorsaresimpleandefficient.Theyexpresstheoperationdirectly,withoutextramethodcalls.Afunctionthatusesdefaultoperatorsisgeneric.Itcanbeusedwithanytypethatsupportstheoperation.

Youcan'

ttellthetypeofobjectsbyreadingthemethodnames（e.g.has_key（）meansadictionary）.Thisisalsoanadvantage.

Usedefaultiteratorsandoperatorsfortypesthatsupportthem,likelists,dictionaries,andfiles.Thebuilt-intypesdefineiteratormethods,too.Preferthesemethod