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POpython coding - Sieve of eratosthenes how to draw from list?
 

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  1. POpython coding - Sieve of eratosthenes how to draw from list?
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    <p>Hi all I have a question im working on in python and seem to be stuck on step 3 and 4. Any help would be great. This is the question:</p> <p>Write a program which implements a function for the sieve of Eratosthenes. (<a href="http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes" rel="nofollow">http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes</a>). The sieve of Eratosthenes is a simple algorithm for finding all prime numbers up to a specified integer. It was created by the ancient Greek mathematician Eratosthenes. The algorithm to find all the prime numbers less than or equal to a given integer n:</p> <ol> <li>Create a list of integers from two to n: 2, 3, 4, ..., n</li> <li>Start with a counter i set to 2, i.e. the first prime number</li> <li>Starting from i+i, count up by i and remove those numbers from the list, i.e. 2*i, 3*i, 4*i, and so on...</li> <li>Find the first number of the list following i. This is the next prime number.</li> <li>Set i to the number found in the previous step</li> <li>Repeat steps 3 and 4 until i is greater than n.</li> <li>All the numbers, which are still in the list, are prime numbers</li> </ol> <p>This is what I have coded so far just don't know how to get the prime numbers from the list and remove the others....:</p> <pre><code>def main(): n = int(input("Enter a limiting number to find the prime numbers smaller than it: ")) num_list = [] num = 1 for i in range(2, n + 1): num = num + 1 num_list.append(num) i = 2 for p in range(2, n): non_prime = num * i #while non_prime &lt; n: if non_prime == num: num_list.remove(num) i = i + 1 print(num_list) main() # Call the main function </code></pre> <p>Thank for your help im banging my head against the wall as we speak.</p>
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