factors.py

def factors(n):
    factors = []

    # This loop weeds out any factors of 2 that are in the number
    while n % 2 == 0:
        factors.append(2)
        n //= 2
    
    # This variable holds the divisor that we're testing
    d = 3

    while d*d <= n:             # Keep looping while d <= sqrt(n)

        while n % d == 0:       # Weed out factors of d
            factors.append(d)   # (remember, if n % d == 0, then d
            n //= d             # is guaranteed to be a prime in this case)

        d += 2                  # Find the next factor

    # If n is not 1 at this point, then n is a prime factor
    if n != 1:
        factors.append(n)

    return factors