class PrimeList:
def __init__(self, initial=0):
self.primelist = [2]
self.primelookup = [0,0,1,1]
self.max_prime = 2
self.initialise_list(initial)
def initialise_list(self,upto):
"Good old Sieve of Eratosthenes"
if upto <= 3:
pass
self.primelookup.extend([0,1] * ((upto-3)//2))
if upto % 2 == 0:
self.primelookup.extend([0])
for i in range(3, upto + 1 , 2):
if self.primelookup[i]:
self.primelist.append(i)
self.max_prime = i
j = i + i
while j <= upto:
self.primelookup[j] = 0
j += i
def __contains__(self,number):
if number < 2:
return False
if number > self.max_prime - 1:
#print "Asking for what I dont have!"
return self._isprime(number)
return self.primelookup[number]
def _isprime(self, number):
for prime in self.primelist:
if prime > number ** .5:
break
if number % prime == 0:
return False
if number < self.max_prime ** 2:
return True
else:
#Brute forcing
for i in range(self.max_prime,number ** .5 + 1, 2):
if number % i == 0:
return False
return True
