PROGRAMAÇÃOFUNCIONAL EM PYTHON

Hugo Tavares

Juarez Bochi

globo.com

THE ELEMENTS OF PROGRAMMINGPrimitive Expressions

Means of CombinationMeans of Abstraction

PARADIGMASImperativo

LógicoOrientado a Objetos

Funcional

PYTHON É FUNCIONAL?

FIRST CLASS FUNCTIONHIGHER-ORDER FUNCTION

HIGHER-ORDER FUNCTION - SORT BYpessoas = [{'nome': 'Adolfo', 'estado': 'MG'}, {'nome': 'Pedro', 'estado': 'RS'}, {'nome': 'Maria', 'estado': 'AC'}]

def por_estado(pessoa1, pessoa2): return cmp(pessoa1['estado'], pessoa2['estado'])

>>> pprint.pprint(sorted(pessoas, cmp=por_estado))[{'estado': 'AC', 'nome': 'Maria'}, {'estado': 'MG', 'nome': 'Adolfo'}, {'estado': 'RS', 'nome': 'Pedro'}]

HIGHER-ORDER FUNCTION - DECORATORdef memoize(fn): cache = {} def newfn(arg): if arg in cache: return cache[arg] else: cache[arg] = fn(arg) return cache[arg] return newfn

APLICAÇÃO DECORATORdef fib(n): if n in (1, 2): return 1 return fib(n - 1) + fib(n - 2)

def fast_fib(n): if n in (1, 2): return 1 return fast_fib(n - 1) + fast_fib(n - 2)

fast_fib = memoize(fast_fib)

if __name__ == '__main__': print(timeit.timeit("import fib; fib.fib(35)", number=1)) print(timeit.timeit("import fib; fib.fast_fib(35)", number=1))

# 3.71057915688# 0.000109195709229

RECURSÃO - MOEDASdef troco(n, moedas): if n == 0: return 1 elif n < 0 or len(moedas) == 0: return 0 else: return troco(n, moedas[1:]) + \ troco(n - moedas[0], moedas)

>>> troco(3, [1, 2])2>>> troco(100, [50, 7])1>>> troco(10, [50, 10, 5, 1, .50, .25, .10, .5, .1])1153

RECURSÃO - FATORIALdef fat(n): if n == 0: return 1 else: return n * fat(n - 1)

"""fat(5)5 * fat(4)5 * (4 * fat(3))5 * (4 * (3 * fat(2)))5 * (4 * (3 * (2 * fat(1)))5 * (4 * (3 * (2 * (1 * fat(0)))5 * (4 * (3 * (2 * (1 * 1))5 * (4 * (3 * (2 * 1))5 * (4 * (3 * 2))5 * (4 * 6)5 * 24120"""

TAIL RECURSIONdef fat(n, acc=1): if n == 0: return acc else: return fat(n - 1, acc * n)

"""fat(5, 1)fat(4, 5)fat(3, 20)fat(2, 60)fat(1, 120)fat(0, 120)120"""

>>> fat(1000) File "", line 5, in fat ...RuntimeError: maximum recursion depth exceeded

TAIL RECURSION OPTIMIZATIONfrom optimization import tail_call_optimized

@tail_call_optimizeddef fat(n, acc=1): if n <= 1: return acc else: return fat(n - 1, acc * n)

>>> fat(1000)402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223

@tail_call_optimized

CURRYINGdef somador(a): def soma(b): return a + b return soma

>>> somador(1)<function soma at 0x100499f50>>>> somador(1)(2)3>>> incr = somador(1)>>> incr(2)3>>> incr(3)4

CURRYING & PARTIALSdef partial(funcao, argumento): def fn(arg): return funcao(argumento, arg) return fn

def to_tag(tag, texto): return "<{tag}>{texto}</{tag}>".format(tag=tag, texto=texto)

negrito = partial(to_tag, 'b')italico = partial(to_tag, 'i')

>>> negrito(italico("oi, python brasil"))"<b><i>oi, python brasil</i></b>"

DATA ABSTRACTION

DATA ABSTRACTIONclass Zero(Natural): def __init__(self): pass

def __repr__(self): return "0"

def __add__(self, other): return other

DATA ABSTRACTIONclass Natural(object): def __init__(self, anterior): self.anterior = anterior

def __repr__(self): return repr(self.anterior) + " + 1"

def __add__(self, other): return self.anterior + other.sucessor()

def sucessor(self): return Natural(anterior=self)

DATA ABSTRACTION>>> zero = Zero()>>> um = zero.sucessor()>>> dois = um.sucessor()>>> um0 + 1>>> dois0 + 1 + 1>>> um + dois0 + 1 + 1 + 1

STOP WRITING CLASSESJack Diederich, PyCon US 2012

http://pyvideo.org/video/880/stop-writing-classes

STOP WRITING CLASSESclass Greeting(object): def __init__(self, greeting="hello"): self.greeting = greeting

def greet(self, name): return "{greet}! {name}".format(greet=self.greeting, name)

>>> hola = Greeting("hola")>>> hola.greet("bob")"hola! bob"

LAZYNESS & GENERATORS

LAZYNESS & GENERATORSdef naturais(): i = 0 while True: yield i i += 1

def pares(): return ifilter(lambda x: x % 2 == 0, naturais())

>>> sum(take(pares(), 10))90

RESUMOCódigo compreensível

Fácil de testarFácil de manterFácil de escalar

REFERÊNCIASStructure and Interpretation of Computer Programs

Functional Programming Principles in ScalaStop Writing Classes" - PyCon US 2012

Códigos usados na palestra:

OBRIGADO!@hltbra@jbochi