random_04.py

def random_choice(rng, options, weights=None):
    """Pick something randomly from a list"""
    if weights is None:
        # Simple case: everything has equal chance
        index = rng.extract_number() % len(options)
        return options[index]
    
    # Complex case: some things are more likely than others
    # Generate random value in [0, sum(weights))
    r = random_float(rng) * sum(weights)
     
    # Find which bucket r falls into
    cumsum = 0
    for option, weight in zip(options, weights):
        cumsum += weight
        if r < cumsum:
            return option