isprime.py

def isprime(n):
	if n<=1:
		return False
	elif n<4:
		return True
	elif n%2==0 or n%3==0:
		return False
	elif n<9:
		return True
	elif n%5==0:
		return False
	else:
		k=5
		while k<((n**0.5)//1+1):
			if n%k==0 or n%(k+2)==0:
				return False
			k=k+6
		return True