Programação Funcional em Python Apresentada na Python Brasil 2012 com Hugo Lopes Tavares

1. PROGRAMAÇÃO
FUNCIONAL EM PYTHON
Hugo Tavares
Juarez Bochi
globo.com

2. THE ELEMENTS OF PROGRAMMING
Primitive Expressions
Means of Combination
Means of Abstraction

3. PARADIGMAS
Imperativo
Lógico
Orientado a Objetos
Funcional

4. PYTHON É FUNCIONAL?

5. FIRST CLASS FUNCTION
HIGHER-ORDER FUNCTION

6. HIGHER-ORDER FUNCTION - SORT BY
pessoas = [{'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'}]

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

8. APLICAÇÃO DECORATOR
def 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

10. RECURSÃO - MOEDAS
def 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

11. RECURSÃO - FATORIAL
def 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 * 24
120
"""

12. TAIL RECURSION
def 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

13. TAIL RECURSION OPTIMIZATION
from optimization import tail_call_optimized
@tail_call_optimized
def fat(n, acc=1):
if n <= 1:
return acc
else:
return fat(n - 1, acc * n)
>>> fat(1000)
402387260077093773543702433923003985719374864210714632543799910429
938512398629020592044208486969404800479988610197196058631666872994
808558901323829669944590997424504087073759918823627727188732519779
505950995276120874975462497043601418278094646496291056393887437886
487337119181045825783647849977012476632889835955735432513185323958
463075557409114262417474349347553428646576611667797396668820291207
379143853719588249808126867838374559731746136085379534524221586593
201928090878297308431392844403281231558611036976801357304216168747
609675871348312025478589320767169132448426236131412508780208000261
683151027341827977704784635868170164365024153691398281264810213092
761244896359928705114964975419909342221566832572080821333186116811
553615836546984046708975602900950537616475847728421889679646244945
160765353408198901385442487984959953319101723355556602139450399736
280750137837615307127761926849034352625200015888535147331611702103
968175921510907788019393178114194545257223865541461062892187960223

14. @tail_call_optimized

15. CURRYING
def 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

16. CURRYING & PARTIALS
def 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>"

17. DATA ABSTRACTION

18. DATA ABSTRACTION
class Zero(Natural):
def __init__(self):
pass
def __repr__(self):
return "0"
def __add__(self, other):
return other

19. DATA ABSTRACTION
class 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)

20. DATA ABSTRACTION
>>> zero = Zero()
>>> um = zero.sucessor()
>>> dois = um.sucessor()
>>> um
0 + 1
>>> dois
0 + 1 + 1
>>> um + dois
0 + 1 + 1 + 1

21. STOP WRITING CLASSES
Jack Diederich, PyCon US 2012
http://pyvideo.org/video/880/stop-writing-classes

22. STOP WRITING CLASSES
class 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"

23. LAZYNESS & GENERATORS

24. LAZYNESS & GENERATORS
def naturais():
i = 0
while True:
yield i
i += 1
def pares():
return ifilter(lambda x: x % 2 == 0, naturais())
>>> sum(take(pares(), 10))
90

25. RESUMO
Código compreensível
Fácil de testar
Fácil de manter
Fácil de escalar

26. REFERÊNCIAS
Structure and Interpretation of Computer Programs
Functional Programming Principles in Scala
Stop Writing Classes" - PyCon US 2012
Códigos usados na palestra:

27. OBRIGADO!
@hltbra
@jbochi