utils.py 文件源码

def factorial(N):
    """Compute the factorial of N.
    If N <= 16, use a fast lookup table; otherwise use scipy.special.factorial
    """
    if N < len(FACTORIALS):
        return FACTORIALS[N]
    elif scipy_special is None:
        raise ValueError("need scipy for computing larger factorials")
    else:
        return int(scipy_special.factorial(N))