is_prime.py

#!/usr/bin/python3

def is_prime(n: int) -> bool:
	"""Primality test using 6k+-1 optimization."""
	if n <= 3:
		return n > 1
	if n % 2 == 0 or n % 3 == 0:
		return False
	i = 5
	while i ** 2 <= n:
		if n % i == 0 or n % (i + 2) == 0:
			return False
		i += 6
	return True