True or false output based on a probability

import random

def decision(probability):
    return random.random() < probability

Given a function rand that returns a number between 0 and 1, you can define decision like this:

bool decision(float probability)
{
   return rand()<probability;
}

Assuming that rand() returns a value in the range [0.0, 1.0) (so can output a 0.0, will never output a 1.0).

Just use PyProbs library. It is very easy to use.

>>> from pyprobs import Probability as pr
>>> 
>>> # You can pass float (i.e. 0.5, 0.157), int (i.e. 1, 0) or str (i.e. '50%', '3/11')
>>> pr.prob(50/100)
False
>>> pr.prob(50/100, num=5)
[False, False, False, True, False]

I use this to generate a random boolean in python with a probability:

from random import randint
n=8 # inverse of probability
rand_bool=randint(0,n*n-1)%n==0

so to expand that :

def rand_bool(prob):
    s=str(prob)
    p=s.index('.')
    d=10**(len(s)-p)
    return randint(0,d*d-1)%d<int(s[p+1:])

I came up with this myself but it seems to work.