#MonthOfCode day 17 - random

day_17.py

import time
current_milli_time = lambda: int(round(time.time() * 1000))

# we use the Factory Design Pattern, RngCreator is the abstract class
class RngCreator(object):
    def createRng(self):
        raise NotImplementedError("Please Implement this method")
    def inputParams(self, p_dict):
        raise NotImplementedError("Please Implement this method")

class LcgCreator(RngCreator):
    #default values
    prod_a, prod_c, prod_m = 22695477,1, 2**32  #parameters used by the Borland C/C++ compiler
    def createRng(self):
        return Lcg(self.prod_a, self.prod_c, self.prod_m)
    def inputParams(self, p_dict):
        self.prod_a, self.prod_c, self.prod_m = p_dict['a'], p_dict['c'],p_dict['m']

class Lcg:
    '''A linear congruential generator (LCG) is an algorithm that yields
    a sequence of randomized numbers calculated with a linear equation.'''
    seed = current_milli_time()
    prev_val = seed
    def __init__(self, a, c, m):
        self.a, self.c, self.m = a,c,m

    def randomRaw( self):
        self.prev_val = (
            self.a * self.prev_val + self.c) % self.m #formula for generating a new pseudo-rand number
        return self.prev_val

    def randint( self, binf, bsup):
        if( bsup<= binf):
            raise ValueError("bsup must be greater than binf")
        random_var = self.randomRaw()
        return binf +(  random_var % (bsup-binf+1) )

def performTestRng( generator ):
    ''' simulates numerous dice throws! '''
    NB_THROWS = 6* 100
    occurences = [ 0 for i in xrange(6) ]
    for n in xrange( NB_THROWS ):
        nb = generator.randint(1,6) 
        print nb,
        for i in range(1,7):
            if(i == nb):
                occurences[i-1]+=1
    print ;
    for i in range(1,7):
        print "nb",i,"occurs",occurences[i-1]," ;",
    print ;

generator1 = LcgCreator().createRng()
print "testing the first RNG:" ; performTestRng( generator1)

custom_creator = LcgCreator()
custom_creator.inputParams(
    {'a':25214903917, 'c':11, 'm':2**48 } ) # parameters used by Java.util.Random
generator2 =custom_creator.createRng()
print "testing the second RNG:" ; performTestRng( generator2)

Instructive!