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Python: Sieve of Eratosthenes method, for computing prime number

Python List: Exercise - 34 with Solution

Write a Python program using Sieve of Eratosthenes method for computing primes upto a specified number.

Note: In mathematics, the sieve of Eratosthenes (Ancient Greek: κόσκινον Ἐρατοσθένους, kóskinon Eratosthénous), one of a number of prime number sieves, is a simple, ancient algorithm for finding all prime numbers up to any given limit.

Python: Sieve of Eratosthenes method, for computing prime number

From Wikipedia Sieve of Eratosthenes: algorithm steps for primes below 121 (including optimization of starting from prime's square).

Sample Solution:-

Python Code:

def prime_eratosthenes(n):
    prime_list = []
    for i in range(2, n+1):
        if i not in prime_list:
            print (i)
            for j in range(i*i, n+1, i):
                prime_list.append(j)

print(prime_eratosthenes(100));

Sample Output: 

2                                                                                                             
3                                                                                                             
5                                                                                                             
7                                                                                                             
11                                                                                                            
-------
79                                                                                                            
83                                                                                                            
89                                                                                                            
97                                                                                                            
None

Flowchart:

Flowchart: Sieve of Eratosthenes method, for computing prime numbers

Python Code Editor:

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

  • The os and os.path modules.
  • The __file__ constant
  • os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
  • os.path.dirname(path) (returns "the directory name of pathname path")
  • os.getcwd() (returns "a string representing the current working directory")
  • os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m