input: def generate_prime_numbers(n):
      """Generate all prime numbers up to a given number n.
      >>> generate_prime_numbers(10)
      2
      3
      5
      7
      >>> generate_prime_numbers(20)
      2
      3
      5
      7
      11
      13
      17
      19
      """
      primes = [True for i in range(n + 1)]
      p = 2
      while (p * p <= n):
          if (primes[p] == True):
              for i in range(p * p, n + 1, p):
                  primes[i] = False
          p += 1
      primes[0] = False
      primes[1] = False
      for p in range(n + 1):
          if primes[p]:
              print(p)
output:     primes = [True for i in range(n + 1)]
      p = 2
      while (p * p <= n):
          if (primes[p] == True):
              for i in range(p * p, n + 1, p):
                  primes[i] = False
          p += 1
      primes[0] = False
      primes[1] = False
      for p in range(n + 1):
          if primes[p]:
              print(p)