Fn.py: enjoy FP in Python

What we are going to talk about?

  fn.py  

Prehistory

• github.com/kachayev/fn.py
• FP with Python
• Lazy evaluation and infinite sequences

Lambdas

Scala

List(1,2,3).map(_*2)

Clojure

(map #(* % 2) '(1 2 3))

Haskell

map (2*) [1,2,3]

Python ???

Lambdas

Python !!!

from fn import _
from fn.iters import zipwith
from itertools import repeat

assert list(map(_ * 2, range(5))) == [0,2,4,6,8]
assert list(filter(_ < 10, [9,10,11])) == [9]
assert list(zipwith(_ + _)([0,1,2], repeat(10))) == [10,11,12]

• code readability
• improve your vision
• keyboard will work longer

Streams

from fn import Stream

s = Stream() << [1,2,3,4,5]
assert list(s) == [1,2,3,4,5]
assert s[1] == 2
assert s[0:2] == [1,2]

s = Stream() << range(6) << [6,7]
assert list(s) == [0,1,2,3,4,5,6,7]

def gen():
    yield 1
    yield 2
    yield 3

s = Stream() << gen << (4,5)
assert list(s) == [1,2,3,4,5]

Streams

And that's it ???

Fibonacci in Haskell

fibs = 0 : 1 : zipWith (+) fibs (tail fibs)

Usage:

Prelude> take 10 fibs
[0,1,1,2,3,5,8,13,21,34]
Prelude> take 20 fibs
[0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181]

Fibonacci in Clojure

user> (def fib (lazy-cat [0 1] (map + fib (rest fib))))
user> (take 10 fib)
(0 1 1 2 3 5 8 13 21 34)
user> (take 20 fib)
(0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181)

Fibonacci in Scala

def fibs: Stream[Int] = 
    0 #:: 1 #:: fibs.zip(fibs.tail).map{case (a,b) => a + b} 

Usage:

scala> fibs(10)
res0: Int = 55
scala> fibs.take(10).toArray
res1: Array[Int] = Array(0, 1, 1, 2, 3, 5, 8, 13, 21, 34)
scala> fibs.take(20).toArray
res2: Array[Int] = Array(0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181)

Fibonacci in Python

And what about Python ???

Fibonacci in Python

from fn import Stream
from fn.iters import take, drop, map
from operator import add

f = Stream()
fib = f << [0, 1] << map(add, f, drop(1, f))

assert list(take(10, fib)) == [0,1,1,2,3,5,8,13,21,34]
assert fib[20] == 6765
assert fib[30:35] == [832040,1346269,2178309,3524578,5702887]

Need more?

• Simple syntax for partial application and composition
• 22 additional itertools recipes
• [TBD] Trampoline decorator
• [TBD] Functional errors-handling
• [TBD] Benchmarks, optimization, C-accelerators

Want to help?

• Use it and enjoy FP
• Post bugs, ideas, advices, patches
• Tell your friends

Thanks for your attention