Python Program for Sieve of Eratosthenes

In this article, we will learn about the solution to the problem statement given below.

Problem statement − We are given a number n, we need to print all primes smaller than or equal to n. Constraint: n is a small number.

Now let’s observe the solution in the implementation below −

Example

def SieveOfEratosthenes(n):
   # array of type boolean with True values in it
   prime = [True for i in range(n + 1)]
   p = 2
   while (p * p <= n):
      # If it remain unchanged it is prime
      if (prime[p] == True):
         # updating all the multiples
         for i in range(p * 2, n + 1, p):
            prime[i] = False
      p += 1
   prime[0]= False
   prime[1]= False
   # Print
   for p in range(n + 1):
      if prime[p]:
         print (p,end=" ")
# main
if __name__=='__main__':
   n = 33
   print ("The prime numbers smaller than or equal to", n,"is")
   SieveOfEratosthenes(n)

Output

The prime numbers smaller than or equal to 33 is
2 3 5 7 11 13 17 19 23 29 31

All the variables are declared in the local scope and their references are seen in the figure above.

Conclusion

In this article, we have learned about how we can make a Python Program for Sieve of Eratosthenes