I'm still trying to understand classes. I've made some progress, I
think, but I don't understand how to use this one. How do I call it,
or any of its functions? It's from the Cookbook, at
<http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/523048>.
Thanks,
Dick Moores
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class PrimeList:
def __init__(self, initial=0):
self.primelist = [2,3]
self.primelookup = [0,0,1,1]
self.max_prime = 3
self.grow_primelist(initial)
def grow_primelist(self,number):
newprimes = []
while self.max_prime <= number:
next = self.nextprime()
newprimes.append(next)
self.max_prime = next
size_difference = self.max_prime -
len(self.primelookup) + 1
self.primelookup.extend([0] * size_difference)
for i in newprimes:
self.primelookup[i]=1
def contains(self,number):
if number < 2:
return 0
if number > len(self.primelookup) - 1:
self.grow_primelist(number)
return self.primelookup[number]
return self.primelookup[number]
def nextprime(self):
i = self.max_prime + 2
while 1:
isprime = True
for prime in self.primelist:
if i % prime == 0:
isprime = False
i += 2
break
if isprime:
self.primelist.append(i)
return(i)
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