lazy-python

A Python Lazy Programming library.

Overview

Lazy Evaluation is among useful features in Functional Programming. This tool help make lazy evaluation in Python easier. The expression is saved in directed graph and evaluated when necessary. The process of evaluation leverage multicore (multiprocessing library in Python) and graph cut algorithm to compute the results in parallel.

Examples

This example illustrate how to calculate Fibnoacci by Lazy Evalution and the cache mechanism of pure function call with the same parameters. By adding parameter "debug=True", it is easy to show the evaluation process step by step.

>>> from lazy import Lazy
>>> def fib(n):
...     return Lazy(int, debug=True)(n) if n <= 1 else fib(n-1) + fib(n-2)
... 
>>> a = fib(10)
>>> a
(((((((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1))+(((1+int(0))+1)+(1+int(0))))+((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1)))+(((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1))+(((1+int(0))+1)+(1+int(0)))))+((((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1))+(((1+int(0))+1)+(1+int(0))))+((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1))))+(((((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1))+(((1+int(0))+1)+(1+int(0))))+((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1)))+(((((1+int(0))+1)+(1+int(0)))+((1+int(0))+1))+(((1+int(0))+1)+(1+int(0))))))
>>> a.eval()
int(0) == 0
(1+0) == 1
(1+1) == 2
(2+1) == 3
(3+2) == 5
(5+3) == 8
(8+5) == 13
(13+8) == 21
(21+13) == 34
(34+21) == 55
55
>>> a
55
>>> b = fib(11)
>>> b
(55+34)
>>> b.eval()
(55+34) == 89
89

Lazy Evaluation uses implicit parallel by multiprocessing. The following example shows how the implicit parallel works by using decorator lazy.

from lazy import lazy
import time

def f(name):
    print('Enter', name)
    time.sleep(5)
    print('Leave', name)

@lazy
def f1():
    f('f1')
    return 1

@lazy
def f2():
    f('f2')
    return 2

@lazy
def f3():
    f('f3')
    return 3

@lazy
def f4():
    f('f4')
    return 4

if __name__ == '__main__':
    s = f1()*f2()+f3()*f4()
    print(s)
    s.eval()
    print(s)

$ time python3 1.py
((f1()*f2())+(f3()*f4()))
Enter f1
Enter f2
Enter f3
Enter f4
Leave f1
Leave f3
Leave f4
Leave f2
14

real    0m5.173s
user    0m0.111s
sys 0m0.049s