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1,800 | that these descriptors store base values as instance stateso they must use leading underscores again so as not to clash with the names of descriptorsas we'll see in the final example of this we could avoid this renaming requirement by storing base values as descriptor state insteadbut that doesn' as directly address da... |
1,801 | elseself __dict__[namevalue powers( print( squareprint( cubex square print( squareor use object * * * the final optioncoding this with __getattribute__is similar to the prior version because we catch every attribute nowthoughwe must also route base value fetches to superclass to avoid looping or extra calls--fetching s... |
1,802 | if you've been reading this book linearlysome of this section is review and elaboration on material covered earlierespecially in for othersthis topic is presented in this context here when introduced __getattr__ and __getattribute__i stated that they intercept undefined and all attribute fetchesrespectivelywhich makes ... |
1,803 | this doeshowevermake object wrappers more work than they used to be when operator overloading methods are part of wrapped object' interface keep in mind that this issue applies only to __getattr__ and __getattribute__ because properties and descriptors are defined for specific attributes onlythey don' really apply to d... |
1,804 | tryx[ __getitem__exceptprint('fail []'tryx __add__exceptprint('fail +'tryx(__call__(implicit via built-inexceptprint('fail ()' __call__(print( __str__()print(x__call__(explicitnot inherited__str__(explicitinherited from type__str__(implicit via built-inwhen run under python as coded__getattr__ does receive variety of i... |
1,805 | must be made new-style by deriving from object to use this method this code' object derivation is optional in because all classes are new-style when run under python xthoughresults for __getattr__ differ--none of the implicitly run operator overloading methods trigger either attribute interception method when their att... |
1,806 | operations are never routed through either attribute interception method in xpython ' new-style classes search for such attributes in classes and skip instance lookup entirely normally named attributes do not this makes delegation-based wrapper classes more difficult to code in ' new-style classes--if wrapped classes m... |
1,807 | def __getattr__(selfattr)return getattr(self personattrdef __repr__(self)return str(self personintercept and delegate delegate all other attrs must overload again (in xif __name__ ='__main__'sue person('sue jones'job='dev'pay= print(sue lastname()sue giveraise print(suetom manager('tom jones' manager __init__ print(tom... |
1,808 | default classic classesbecause operator overloading attributes are routed through this methodand such classes do not inherit default for __repr__c:\codepy - getattr-delegate py jones [personsue jones jones [persontom jones switching to __getattribute__ won' help here either--like __getattr__it is not run for operator o... |
1,809 | return lambda percentperson giveraise(percent elsereturn getattr(personattrdef __repr__(self)person object __getattribute__(self'person'return str(personwhen this alternative runsour object prints properlybut only because we've added an explicit __repr__ in the wrapper--this attribute is still not routed to our generic... |
1,810 | used to intercept all attributes generically to understand this codeit' crucial to notice that the attribute assignments inside the __init__ constructor method trigger property setter methods too when this method assigns to self namefor exampleit automatically invokes the setname methodwhich transforms the value and as... |
1,811 | return self __acct[:- '***def setacct(selfvalue)value value replace('-'''if len(value!self acctlenraise typeerror('invald acct number'elseself __acct value acct property(getacctsetacctdef remainget(self)return self retireage self age remain property(remaingetcould be methodnot attr unless already using as attr testing ... |
1,812 | sue remain exceptprint("can' set sue remain"trysue acct ' exceptprint('bad acct for sue'here is the output of our self-test code on both python and xagainthis is the same for all versions of this exampleexcept for the tested class' name trace through this code to see how the class' methods are invokedaccounts are displ... |
1,813 | added the required object derivation to the main descriptor classes for compatibility (they can be omitted for code to be run in onlybut don' hurt in xand aid portability if present)file validate_descriptors pyusing shared descriptor state class cardholder(object)acctlen retireage def __init__(selfacctnameageaddr)self ... |
1,814 | output as shown for properties earlierexcept that the name of the class in the first line variesc:\codepython validate_tester py validate_descriptors same output as propertiesexcept class name option validating with per-client-instance state unlike in the prior property-based variantthoughin this case the actual name v... |
1,815 | stored as per-instance data instead of descriptor instance dataperhaps using the same __x naming convention as the property-based equivalent to avoid name clashes in the instance-- more important factor this timeas the client is different class with its own state attributes here are the required coding changesit doesn'... |
1,816 | (bob remains bob)and other tests work as beforec:\codepy - validate_tester py validate_descriptors [usingbobbob_smith ** main st suesue_jones ** main st bobbob_smith ** main st :\codepy - validate_tester py validate_descriptors same output as propertiesexcept class name one small caveat hereas codedthis version doesn' ... |
1,817 | as for the property and descriptor versions of this exampleit' critical to notice that the attribute assignments inside the __init__ constructor method trigger the class' __setattr__ method too when this method assigns to self namefor exampleit automatically invokes the __setattr__ methodwhich transforms the value and ... |
1,818 | acct mangled to _acct if value raise valueerror('invalid age'elif name ='acct'name '_acctvalue value replace('-'''if len(value!self acctlenraise typeerror('invald acct number'elif name ='remain'raise typeerror('cannot set remain'self __dict__[namevalue avoid looping (or via objectwhen this code is run with either test ... |
1,819 | def __getattribute__(selfname)superget object __getattribute__ don' loopone level up if name ='acct'on all attr fetches return superget(self'acct')[:- '***elif name ='remain'return superget(self'retireage'superget(self'age'elsereturn superget(selfnamenameageaddrstored def __setattr__(selfnamevalue)if name ='name'on all... |
1,820 | bute__ and properties and descriptors isn' all this feature comparison just kind of argumenttest your knowledgeanswers the __getattr__ method is run for fetches of undefined attributes only ( those not present on an instance and not inherited from any of its classesby contrastthe __getattribute__ method is called for e... |
1,821 | new features tend to offer alternativesbut do not fully subsume what came before no it isn' to quote from python namesake monty python' flying circusan argument is connected series of statements intended to establish proposition no it isn' yes it isit' not just contradiction lookif argue with youi must take up contrary... |
1,822 | decorators in the advanced class topics of this book ()we met static and class methodstook quick look at the decorator syntax python offers for declaring themand previewed decorator coding techniques we also met function decorators briefly in while exploring the property built-in' ability to serve as oneand in while st... |
1,823 | timeproviding layer of logic that can manage classesor the instances created by later calls to them in shortdecorators provide way to insert automatically run code at the end of function and class definition statements--at the end of def for function decoratorsand at the end of class for class decorators such code can ... |
1,824 | function objectsand class decorators can be used to manage both class instances and classes themselves by returning the decorated object itself instead of wrapperdecorators become simple post-creation step for functions and classes regardless of the role they playdecorators provide convenient and explicit way to code t... |
1,825 | function calls that may be arbitrarily far-removed from the subject functions or classes decorators are applied oncewhen the subject function or class is definedit' not necessary to add extra code at every call to the class or functionwhich may have to be changed in the future because of both of the prior pointsdecorat... |
1,826 | let' get started with first-pass look at decoration behavior from symbolic perspective we'll write real and more substantial code soonbut since most of the magic of decorators boils down to an automatic rebinding operationit' important to understand this mapping first function decorators function decorators have been a... |
1,827 | @staticmethod def meth)meth staticmethod(methclass @property def name(self)name property(namein both casesthe method name is rebound to the result of built-in function decoratorat the end of the def statement calling the original name later invokes whatever object the decorator returns in these specific casesthe origin... |
1,828 | in skeleton termshere' one common coding pattern that captures this idea--the decorator returns wrapper that retains the original function in an enclosing scopedef decorator( )def wrapper(*args)use and args (*argscalls original function return wrapper on decoration on wrapped function call @decorator def func(xy)func d... |
1,829 | class @decorator def method(selfxy) instance not in argsmethod decorator(methodrebound to decorator instance when coded this waythe decorated method is rebound to an instance of the decorator classinstead of simple function the problem with this is that the self in the decorator' __call__ receives the decora tor class ... |
1,830 | function decorators proved so useful that the model was extended to allow class decoration as of python and they were initially resisted because of role overlap with metaclassesin the endthoughthey were adopted because they provide simpler way to achieve many of the same goals class decorators are strongly related to f... |
1,831 | process class return @decorator class cc decorator(cto instead insert wrapper layer that intercepts later instance creation callsreturn different callable objectdef decorator( )save or use class return different callablenested defclass with __call__etc @decorator class cc decorator(cthe callable returned by such class ... |
1,832 | as for function decoratorssome callable type combinations work better for class decorators than others consider the following invalid alternative to the class decorator of the prior exampleclass decoratordef __init__(selfc)on decoration self def __call__(self*args)on instance creation self wrapped self (*argsreturn sel... |
1,833 | run on later calls to support multiple nested steps of augmentation this waydecorator syntax allows you to add multiple layers of wrapper logic to decorated function or method when this feature is usedeach decorator must appear on line of its own decorator syntax of this form@ @ @ def )runs the same as the followingdef... |
1,834 | def ( )return def ( )return def ( )return @ @ @ def func()print('spam'func(func ( ( (func))prints "spamthe same syntax works on classesas do these same do-nothing decorators when decorators insert wrapper function objectsthoughthey may augment the original function when called--the following concatenates to its result ... |
1,835 | returns the actual decorator the returned decorator in turn returns the callable run later for calls to the original function namedef (arg) decorator(ab)(frebind to result of decorator' return value ( essentially calls decorator(ab)( )( decorator arguments are resolved before decoration ever occursand they are usually ... |
1,836 | class cc decorator(cas long as we return the original decorated object this way instead of proxywe can manage functions and classes themselvesnot just later calls to them we'll see more realistic examples later in this that use this idea to register callable objects to an api with decoration and assign attributes to fu... |
1,837 | do not require new-style classessome hex addresses have also been shortened to protect the sighted)from decorator import spam spam( call to spam really calls the tracer wrapper object spam(' '' '' 'call to spam abc invokes __call__ in class spam calls number calls in wrapper state information spam when runthe tracer cl... |
1,838 | the last example of the prior section raises an important issue function decorators have variety of options for retaining state information provided at decoration timefor use during the actual function call they generally need to support multiple decorated objects and multiple callsbut there are number of ways to imple... |
1,839 | call to eggs while useful for decorating functionsthis coding scheme still has issues when applied to methods-- shortcoming we'll address in later revision enclosing scopes and globals closure functions--with enclosing def scope references and nested defs--can often achieve the same effectespecially for static data lik... |
1,840 | call to eggs call to eggs enclosing scopes and nonlocals shared global state may be what we want in some cases if we really want per-function counterthoughwe can either use classes as beforeor make use of closure ( factoryfunctions and the nonlocal statement in python xdescribed in because this new statement allows enc... |
1,841 | finallyif you are not using python and don' have nonlocal statement--or you want your code to work portably on both and --you may still be able to avoid globals and classes by making use of function attributes for some changeable state instead in all pythons since we can assign arbitrary attributes to functions to atta... |
1,842 | questionswhere their visibility outside callables becomes an asset as changeable state associated with context of usethey are equivalent to enclosing scope nonlocals as usualchoosing from multiple tools is an inherent part of the programming task because decorators often imply multiple levels of callablesyou can combin... |
1,843 | recognize this as an adaptation of our person class resurrected from the object-oriented tutorial in )class persondef __init__(selfnamepay)self name name self pay pay @tracer def giveraise(selfpercent)self pay *( percentgiveraise tracer(giveraise@tracer def lastname(self)return self name split()[- lastname tracer(lastn... |
1,844 | to self when method name is bound to simple function onlywhen it is an instance of callable classthat class' instance is passed instead technicallypython makes bound method object containing the subject instance only when the method is simple functionnot when it is callable instance of another class using nested functi... |
1,845 | def giveraise(selfpercent)self pay *( percent@tracer def lastname(self)return self name split()[- print('methods 'bob person('bob smith' sue person('sue jones' print(bob namesue namesue giveraise print(int(sue pay)print(bob lastname()sue lastname()giveraise tracer(giveraiseoncall remembers giveraise lastname tracer(las... |
1,846 | attr descriptor( subject( attr roughly runs descriptor __get__(subject attrxsubjectdescriptors may also have __set__ and __del__ access methodsbut we don' need them here more relevant to this topicbecause the descriptor' __get__ method receives both the descriptor class instance and subject class instance when invokedi... |
1,847 | runs __get__ then __call__ runs tracer __get__ firstbecause the giveraise attribute in the person class has been rebound to descriptor by the method function decorator the call expression then triggers the __call__ method of the returned wrapper objectwhich in turn invokes tracer __call__ in other wordsdecorated method... |
1,848 | self calls self meth meth def __get__(selfinstanceowner)on method fetch def wrapper(*args**kwargs)on method callproxy with self+inst self calls + print('call % to % (self callsself meth __name__)return self meth(instance*args**kwargsreturn wrapper class person@tracer def giveraise(selfpercent)applies to class methods g... |
1,849 | self alltime +elapsed print('% (self func __name__elapsedself alltime)return result @timer def listcomp( )return [ for in range( )@timer def mapcall( )return force(map((lambda xx )range( ))result listcomp( time for this callall callsreturn value listcomp( listcomp( listcomp( print(resultprint('alltime %slistcomp alltim... |
1,850 | decorators versus per-call timing for comparisonsee for nondecorator approach to timing iteration alternatives like these as reviewwe saw two per-call timing techniques therehomegrown and library--here deployed to time the list comprehension case of the decorator' test codethough incurring extra costs for management co... |
1,851 | iterable without iteratingat the same timeadding this list call in too charges map with an unfair penalty-the map test' results would include the time required to build two listsnot one to work around thisthe script selects map enclosing function per the python version number in sysin xpicking listand in using no-op fu... |
1,852 | the decorator argument and the original functionand returns the callable oncallwhich ultimately invokes the original function on later calls because this structure creates new decorator and oncall functionstheir enclosing scopes are per-decoration state retention we can put this structure to use in our timer to allow l... |
1,853 | def mapcall( )return force(map((lambda xx )range( ))for func in (listcompmapcall)result func( time for this callall callsreturn value func( func( func( print(resultprint('alltime % \nfunc alltimetotal time for all calls print('**map/comp %sround(mapcall alltime listcomp alltime )againto make this fairmap is wrapped in ... |
1,854 | return [ for in range( ) listcomp( =listcomp listcomp( =listcomp listcomp( =listcomp listcomp alltime as isthis timing function decorator can be used for any functionboth in modules and interactively in other wordsit automatically qualifies as general-purpose tool for timing code in our scripts watch for another exampl... |
1,855 | instances {def singleton(aclass)on decoration def oncall(*args**kwargs)on instance creation if aclass not in instancesone dict entry per class instances[aclassaclass(*args**kwargsreturn instances[aclassreturn oncall to use thisdecorate the classes for which you want to enforce single-instance model (for referenceall th... |
1,856 | the none check could use is instead of =herebut it' trivial test either way) onlynonlocal def singleton(aclass)instance none def oncall(*args**kwargs)nonlocal instance if instance =noneinstance aclass(*args**kwargsreturn instance return oncall on decoration on instance creation and later nonlocal one scope per class in... |
1,857 | way for examplein the __getattr__ operator overloading method is shown as way to wrap up entire object interfaces of embedded instancesin order to implement the delegation coding pattern we saw similar examples in the managed attribute coverage of the prior recall that __getattr__ is run when an undefined attribute nam... |
1,858 | def __getattr__(selfattrname)print('traceattrnameself fetches + return getattr(self wrappedattrnamereturn wrapper use enclosing scope name catches all but own attrs delegate to wrapped obj if __name__ ='__main__'@tracer class spamdef display(self)print('spam! @tracer class persondef __init__(selfnamehoursrate)self name... |
1,859 | [ tracename bob tracepay tracename sue tracepay tracename bob tracepay [ notice how there is one wrapper class with state retention per decorationgenerated by the nested class statement in the tracer functionand how each instance gets its own fetches counter by virtue of generating new wrapper instance as we'll see ahe... |
1,860 | syntax@tracer class personbob person('bob' sue person('sue'rate= hours= decorator approach class personnondecorator approach bob wrapper(person('bob' )sue wrapper(person('sue'rate= hours= )assuming you will make more than one instance of classand want to apply the augmentation to every instance of classdecorators will ... |
1,861 | curiouslythe decorator function in this example can almost be coded as class instead of functionwith the proper operator overloading protocol the following slightly simplified alternative works similarly because its __init__ is triggered when the decorator is applied to the classand its __call__ is triggered when subje... |
1,862 | but not per class instancesuch that only the last instance is retained the solutionas in our prior class blunder for decorating methodslies in abandoning class-based decorators the earlier function-based tracer version does work for multiple instancesbecause each instance construction call makes new wrapper instanceins... |
1,863 | decorating function with logic that intercepts later callswe could simply pass the function and its arguments into manager that dispatches the calldef func(xy)result tracer(func( )nondecorator version def tracer(funcargs)func(*argsspecial call syntax @tracer def func(xy)result func( decorator version rebinds namefunc t... |
1,864 | basis that saidnone of these is very serious issue for most programsdecorationsuniformity is an assetthe type difference is unlikely to matterand the speed hit of the extra calls will be insignificant furthermorethe latter of these occurs only when wrappers are usedcan often be negated if we simply remove the decorator... |
1,865 | and against constructor functions in classes--prior to the introduction of __init__ methodsprogrammers achieved the same effect by running an instance through method manually when creating it ( =class(init()over timethoughdespite being fundamentally stylistic choicethe __init__ syntax came to be universally preferred b... |
1,866 | for name in registryprint(name'=>'registry[name]type(registry[name])print('\nmanual calls:'print(spam( )print(ham( ) eggs( print(xinvoke objects manually later calls not intercepted print('\nregistry calls:'for name in registryprint(name'=>'registry[name]( )invoke from registry when this code is run the decorated objec... |
1,867 | spam marked true def annotate(text)def decorate(func)func label text return func return decorate @annotate('spam data'def spam(ab)return samebut value is decorator argument spam annotate)(spamspam( )spam label ( 'spam data'such decorators augment functions and classes directlywithout catching later calls to them we'll ... |
1,868 | exceptionalong with an error messagethe exception may be caught in try or allowed to terminate the script here is the codealong with self test at the bottom of the file it will work under both python and ( and laterbecause it employs version-neutral print and raise syntaxthough as coded it catches built-insdispatch to ... |
1,869 | self label label accesses inside the subject class self data start not interceptedrun normally def size(self)return len(self datamethods run with no checking def double(self)because privacy not inherited for in range(self size())self data[iself data[ def display(self)print('% =% (self labelself data) doubler(' is'[ ] d... |
1,870 | this code is bit complexand you're probably best off tracing through it on your own to see how it works to help you studythoughhere are few highlights worth mentioning inheritance versus delegation the first-cut privacy example shown in used inheritance to mix in __setattr__ to catch accesses inheritance makes this dif... |
1,871 | the __setattr__ method in this code relies on an instance object' __dict__ attribute namespace dictionary in order to set oninstance' own wrapped attribute as we learned in the prior this method cannot assign an attribute directly without looping howeverit uses the setattr built-in instead of __dict__ to set attributes... |
1,872 | are accessible)but not under public (all undeclared names are inaccessibleagainstudy this code on your own to get feel for how this works notice that this scheme adds an additional fourth level of state retention at the topbeyond that described in the preceding sectionthe test functions used by the lambdas are saved in... |
1,873 | def public(*attributes)return accesscontrol(failif=(lambda attrattr not in attributes)see the prior example' self-test code for usage example here' quick look at these class decorators in action at the interactive promptthey work the same in and for attributes referenced by explicit name like those tested here as adver... |
1,874 | besides generalizingthis version also makes use of python' __x pseudoprivate name mangling feature (which we met in to localize the wrapped attribute to the proxy control classby automatically prefixing it with this class' name this avoids the prior version' risk for collisions with wrapped attribute that may be used b... |
1,875 | operationsunless they are redefined in the proxy clients that do not use operator overloading are fully supportedbut others may require additional code in importantlythis is not new-style class issue hereit' python version issue--the same code runs differently and fails in only because the nature of the wrapped object'... |
1,876 | person object correctlyc:\codec:\python \python from access import private @private('age'class persondef __init__(self)self age def __str__(self)return 'personstr(self agedef __add__(selfyrs)self age +yrs person( age typeerrorprivate attribute fetchage print(xperson print(xperson name validations fail correctly __getat... |
1,877 | _oninstance__wrapped age though calls by name work normally break privacy to view result in other wordsthis is matter of built-in operations versus explicit callsit has little to do with the actual names of the methods involved just for built-in operationspython skips step for ' new-style classes using the alternative ... |
1,878 | return ondecorator mix-in superclasses alternativelythese methods can be inserted by common superclass --given that there are dozens of such methodsan external class may be better suited to the taskespecially if it is general enough to be used in any such interface proxy class either of the following mix-in class schem... |
1,879 | return self _wrapped(*args**kargsplus any others needed def accesscontrol(failif)def ondecorator(aclass)class oninstance(builtinsmixin)and use self _wrapped instead of self __wrapped def __getattr__(selfattr)def __setattr__(selfattrvalue)either one of these superclass mix-ins will be extraneous codebut must be implemen... |
1,880 | for attr in builtinsexec('__%s__ proxydesc("__%s__")(attrattr)this coding may be the most concisebut also the most implicit and complexand is fairly tightly coupled with its subclasses by the shared name the loop at the end of this class is equivalent to the followingrun in the mix-in class' local scope--it creates des... |
1,881 | decorator this is why this extension is omitted in our codethere are potentially more than such methodsbecause all its classes are new-styledelegation-based code is more difficult--though not necessarily impossible--in python implementation alternatives__getattribute__ insertscall stack inspection although redundantly ... |
1,882 | set of classes supported is even further limitedinserting methods will break clients that are already using __setattr__ or __getattribute__ of their own worsethis scheme does not address the built-in operation attributes issue described in the prior sectionbecause __getattribute__ is also not run in these contexts in o... |
1,883 | do wish to regulate attribute access in order to eliminate coding mistakesor happen to be soon-to-be-ex- ++-or-java programmermost things are possible with python' operator overloading and introspection tools examplevalidating function arguments as final example of the utility of decoratorsthis section develops functio... |
1,884 | convenientclass person@rangetest(percent=( )use decorator to validate def giveraise(selfpercent)self pay int(self pay ( percent)isolating validation logic in decorator simplifies both clients and future maintenance notice that our goal here is different than the attribute validations coded in the prior final example he... |
1,885 | file rangetest _test py from __future__ import print_function from rangetest import rangetest print(__debug__false if "python - main py@rangetest(( )persinfo rangetest)(persinfodef persinfo(nameage)age must be in print('% is % years old(nameage)@rangetest([ ][ ][ ]def birthday(mdy)print('birthday { }/{ }/{ }format(mdy)... |
1,886 | birthday typeerrorargument not in running python with its - flag at system command line will disable range testingbut also avoid the performance overhead of the wrapping layer--we wind up calling the original undecorated function directly assuming this is debugging tool onlyyou can use this flag to optimize your progra... |
1,887 | all pargs match first expected args by position the rest must be in kargs or be omitted defaults expected list(allargspositionals expected[:len(pargs)for (argname(lowhigh)in argchecks items()for all args to be checked if argname in kargswas passed by name if kargs[argnamehigherrmsg '{ argument "{ }not in { { }errmsg er... |
1,888 | #persinfo('bob' #persinfo(age= name='bob'#birthday( = = test methodspositional and keyword class persondef __init__(selfnamejobpay)self job job self pay pay giveraise rangetest)(giveraise@rangetest(percent=( )percent passed by name or position def giveraise(selfpercent)self pay int(self pay ( percent)bob person('bob sm... |
1,889 | argument "ddefaulted argument "cdefaulted argument "bdefaulted argument "cdefaulted argument "bdefaulted argument "cdefaulted argument "bdefaulted on validation errorswe get an exception as before when one of the method test lines is uncommentedunless the - command-line argument is passed to python to disable the decor... |
1,890 | many arguments to be matched against the expected arguments so obtained from the function' introspection apidef catcher(*pargs**kargs)print('% % (pargskargs)catcher( ( ){catcher( = = = ( ){' ' ' ' ' ' arguments at calls the function object' api is available in older pythonsbut the func __code__ attribute is named func ... |
1,891 | nowgiven these constraints and assumptionswe can allow for both keywords and omitted default arguments in the call with this algorithm when call is interceptedwe can make the following assumptions and deductions let be the number of passed positional argumentsobtained from the length of the *pargs tuple all positional ... |
1,892 | omitargs( = = = these only failthoughwhere we try to invoke the original functionat the end of the wrapper while we could try to imitate python' argument matching to avoid thisthere' not much reason to do so--since the call would fail at this point anyhowwe might as well let python' own argument-matching logic detect t... |
1,893 | of the expected arguments list)but we'll pass on such an extension here decorator nesting finallyand perhaps most subtlythis code' approach does not fully support use of decorator nesting to combine steps because it analyzes arguments using names in function definitionsand the names of the call proxy function returned ... |
1,894 | def func( :( )bc:( ))print( cthat isthe range constraints would be moved into the function itselfinstead of being coded externally the following script illustrates the structure of the resulting decorators under both schemesin incomplete skeleton code for brevity the decorator arguments code pattern is that of our comp... |
1,895 | 'll leave fleshing out the rest of the annotation-based version as suggested exerciseits code would be identical to that of our complete solution shown earlierbecause range-test information is simply on the function instead of in an enclosing scope reallyall this buys us is different user interface for our tool--it wil... |
1,896 | raise typeerror(errmsgelseassume not passeddefault return func(*pargs**kargsreturn oncall return ondecorator @typetest( =intc=floatdef func(abcd)func typetest)(funcfunc( func('spam' ok triggers exception correctly using function annotations instead of decorator arguments for such decoratoras described in the prior sect... |
1,897 | as we also learnedclass decorators can be used to manage classes themselvesrather than just their instances because this functionality overlaps with metaclasses--the topic of the next and final technical you'll have to read ahead for the conclusion to this storyand that of this book at large firstthoughlet' work throug... |
1,898 | subclasses that provide expected methods can often provide similar generalization routes as well test your knowledgeanswers here' one way to code the first question' solutionand its output (though some methods may run too fast to register reported timethe trick lies in replacing nested classes with nested functionsso t... |
1,899 | def listcomp( )return [ for in range( )like listcomp timer)(listcomplistcomptriggers oncall @timer('[mmm]==>'def mapcall( )return force(map((lambda xx )range( ))list(for views for func in (listcompmapcall)result func( time for this callall callsreturn value func( print(resultprint('alltime % \nfunc alltimetotal time fo... |
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