Extensible biased number generator - Python

Question

I am trying to get a random number generator that will be biased in that it takes a number, and prints a number that is likely to be close. Here's what I have now:

def biasedRandom(rangen, rangex, target, biaslevel=1):
    if rangen > rangex:
        raise ValueError("Min value is less than max value.")
        return
    if not target in range(rangen, rangex):
        raise ValueError("Bias target not inside range of random.")
        return

    num = random.randint(rangen, rangex)
    for i in range(biaslevel):
        distance = abs(num - target)
        num -= random.randint(0, distance)

    return num

This works pretty well, however it has on occasion given completely outrageous numbers; eg it once gave -246174068358 for (1,100,30,60) . I figure there is just a bug in there that I am not seeing.

Thanks in advance.

Answer 1

raise exits the function - you do not need to follow raise with return

target in range(lo, hi) is inefficient; why not lo <= target < hi?

Edit:

import random
def biasedRandom(lo, hi, target, steps=1):
    if lo >= hi:
        raise ValueError("lo should be less than hi")
    elif target < lo or target >= hi:
        raise ValueError("target not in range(lo, hi)")
    else:
        num = random.randint(lo, hi)
        for i in range(steps):
            num += int(random.random() * (target - num))
        return num

As steps is increased, this will pretty rapidly converge on target; you might want to do some trial distributions to make sure that you are getting what you expected, or try using random.gauss instead.

Answer 2

在计算num的最后一行，你是否在想这样的事情？

    num = abs(num - random.randint(0,distance))