Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå
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Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Àëåêñàíäð Ìèõàéëîâ Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè Ïðîñòåéøàÿ ôóíêöèÿ íà Python: > > def empty_func () : .. pass Ôóíêöèè îáúÿâëÿþòñÿ ñ êëþ÷åâûì ñëîâîì def Ôóíêöèÿ - ýòî îáúåêò Ïóñòûå ôóíêöèè íåäîïóñòèìû Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè Áîëåå ñëîæíàÿ ôóíêöèÿ > > def gcd (a , b ) : .. """ Greatest Common .. Divisor """ # docstring .. while a ! = 0 : .. a , b = b %a , a .. return b docstring ìîæíî ïîëó÷èòü òàê: print gcd . __doc__ Ôóíêöèÿ áåç return âîçâðàùàåò ñïåöèàëüíîå çíà÷åíèå None Ïàðàìåòðû â ôóíêöèè ïåðåäàþòñÿ ïî-õèòðîìó Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ïåðåäà÷à ïàðàìåòðîâ Call by object, call by sharing, call by object reference > > def magic ( v ) : .. v . append ( " Blue " ) .. > > list = [ " Red " , " Green "] > > magic ( list ) > > print list [ ' Red ' , ' Green ' , ' Blue '] > > def magic2 ( v ) : .. v = [ " Hue " , " Saturation " , " Value " ] .. > > magic2 ( list ) > > print list [ ' Red ' , ' Green ' , ' Blue '] Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè Ôóíêöèè ìîæíî ïðèñâàèâàòü: > > d = gcd > > print d ( 14 , 7 ) 7 Áëàãîäàðÿ êîðòåæàì, èç ôóíêöèè ìîæíî âîçâðàùàòü ìíîæåñòâî ýëåìåíòîâ: > > def multiout () : .. return 1 , 2 , 3 > > print multiout () (1 , 2 , 3 ) Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Îáëàñòü âèäèìîñòè - Scope  ëþáîé ìîìåíò âûïîíåíèÿ ïðîãðàììû ñóùåñòâóåò, êàê ìèíèìóì, 3 îáëàñòè âèäèìîñòè: Ëîêàëüíàÿ Ñðåäíÿÿ (ãëîáàëüíûå èìåíà ìîäóëÿ) Âíåøíÿÿ (âñòðîåííûå èìåíà) Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè Ïåðåäà÷à íåèçâåñòíîãî êîëè÷åñòâà ïàðàìåòðîâ: > > def avg ( * args ) : .. sum = 0 . 0 .. for arg in args : .. sum + = arg .. return sum / len ( args ) .. > > avg (1 , 2 ) 1.5 > > avg (3 , 5 , 2 ) 3 . 3333333333333335 Òàêæå ìîæíî ïåðåäàâàòü èìåíîâàííûå ïàðàìåòðû.  òàêîì ñëó÷àå, èçìåíÿåòñÿ ñèãíàòóðà: > > def avg ( * * args ) : Òåïåðü ðàáîòà ñ args àíàëîãè÷íà ðàáîòå ñî ñëîâàðåì Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè Ïàðàìåòðû ïî-óìîë÷àíèþ: > > def greet ( adr = " mr . " , name = " X " ) : .. print " Hello " + adr + name + " ! " .. > > greet ( " mrs . " , " Anderson " ) # Íîðìàëüíûé âûçîâ Hello mrs . Anderson ! > > greet ( name = " Gates " ) # Èìåíîâàííûé ïàðàìåòð Hello mr . Gates ! > > greet () # Âûçîâ ñ ïàðàìåòðàìè ïî - óìîë÷àíèþ Hello mr .X ! Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ëÿìáäà-ôóíêöèè Ëÿìáäû ìîæíî âûçûâàòü ñðàçó ïîñëå îïðåäåëåíèÿ > > ( lambda x : x * x )( 5 ) 25 Ôóíêöèè ìîæíî çàäàâàòü ÷åðåç ëÿìáäû > > foo = lambda x : x * x > > print foo ( 7 ) 49 Ëÿìáäà-ôóíêöèÿ - íå èìåíîâàííàÿ ôóíêöèÿ Ôóíêöèè â Python - îáúåêòû ïåðâîãî êëàññà Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Çàìûêàíèÿ Çàìûêàíèå (àíãë. closure) â ïðîãðàììèðîâàíèè - ïðîöåäóðà, êîòîðàÿ ññûëàåòñÿ íà ñâîáîäíûå ïåðåìåííûå â ñâîåì ëåêñè÷åñêîì êîíòåêñòå. >> .. .. .. .. .. >> >> 15 >> >> 20 def make_adder ( x ) : def adder ( n ) : # Çàõâàò ïåðìåííîé " x " èç âíåøíåãî êîíòåêñòà return x + n return adder f = make_adder ( 10 ) print f ( 5 ) # 15 f = make_adder ( 15 ) print f ( 5 ) # 20 Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå â Python Ýëåìåíòû ôóíêöèîíàëüíîãî ïðîãðàììèðîâàíèÿ â Python Ôóíêöèè âûñøèõ ïîðÿäêîâ Ñïèñî÷íûå âûðàæåíèÿ Ðåêóðñèÿ Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè âûñøèõ ïîðÿäêîâ Ôóíêöèÿ map() ïîçâîëÿåò îáðàáàòûâàòü îäíó èëè íåñêîëüêî ïîñëåäîâàòåëüíîñòåé ñ ïîìîùüþ çàäàííîé ôóíêöèè: > > list1 = [7 , 2 , 3 , 10 , 12 ] > > list2 = [ -1 , 1 , -5 , 4 , 6 ] > > map ( lambda x , y : x *y , list1 , list2 ) [ -7 , 2 , - 15 , 40 , 72 ] Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè âûñøèõ ïîðÿäêîâ Ôóíêöèÿ lter() ïîçâîëÿåò ôèëüòðîâàòü çíà÷åíèÿ ïîñëåäîâàòåëüíîñòè.  ðåçóëüòèðóþùåì ñïèñêå òîëüêî òå çíà÷åíèÿ, äëÿ êîòîðûõ çíà÷åíèå ôóíêöèè äëÿ ýëåìåíòà èñòèííî: > > list = [ 10 , 4 , 2 , -1 , 6 ] > > filter ( lambda x : x < 5 , list ) [4 , 2 , - 1 ] Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ôóíêöèè âûñøèõ ïîðÿäêîâ Äëÿ îðãàíèçàöèè öåïî÷å÷íûõ âû÷èñëåíèé â ñïèñêå ìîæíî èñïîëüçîâàòü ôóíêöèþ reduce(): > > list = [2 , 3 , 4 , 5 , 6 ] > > reduce ( lambda res , x : res *x , list , 1 ) 720 Âû÷èñëåíèÿ ïðîèñõîäÿò â ñëåäóþùåì ïîðÿäêå: ((((1*2)*3)*4)*5)*6 Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ñïèñî÷íûå âûðàæåíèÿ - List comprehension > > S = [ x * * 2 for x in range ( 10 ) ] > > V = [ 2 * * i for i in range ( 10 ) ] > > M = [ x for x in S if x % 2 = = 0 ] >> > > print S ; print V ; print M [0 , 1 , 4 , 9 , 16 , 25 , 36 , 49 , 64 , 81 ] [1 , 2 , 4 , 8 , 16 , 32 , 64 , 128 , 256 , 512 ] [0 , 4 , 16 , 36 , 64 ] Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå List comprehension vs map and lter Lc áûñòðåå, åñëè â map íåîáõîäèìî ïåðåäàâàòü ëÿìáäó: python - mtimeit - s ' xs = range ( 10 ) ' ' map ( lambda x : x +2 , xs ) ' 100000 loops , best of 3 : 4 . 24 usec per loop python - mtimeit - s ' xs = range ( 10 ) ' '[ x + 2 for x in xs ] ' 1000000 loops , best of 3 : 1 . 74 usec per loop Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå functools functools - ìîäóëü ôóíêöèé âûñøåãî ïîðÿäêà. @functools.total _ordering (cls) äåêîðàòîð, ïî îäíîìó èëè áîëåå îïåðàòîðó ñðàâíåíèÿ ãåíåðèðóåò îñòàëüíûå @functools.lru _cache(maxsize) äåêîðàòîð, êåøèðóåò äî maxsize âûçîâîâ ôóíêöèè functools.partial(func, ∗args, ∗ ∗ keywords) Ñîçäàåò partial îáúåêò, êîòîðûé âåäåò ñåáÿ êàê func ñ àðãóìåíòàìè args è keywords. Ïðèìåð: > > from functools import partial > > basetwo = partial ( int , base = 2 ) > > basetwo ( ' 10010 ') 18 Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå Ñïàñèáî çà âíèìàíèå! Àëåêñàíäð Ìèõàéëîâ Python: ôóíêöèè, ôóíêöèîíàëüíîå ïðîãðàììèðîâàíèå
