input: from typing import List
  
  
  def print_pattern() -> str:
      """ Produces an output that prints a 7x7 grid of characters where every 
      character at positions where the sum of its row and column index is even 
      is '#' and at positions where the sum is odd is ' ' (space).
      >>> print_pattern()
      # # # # #
       # # # # #
      # # # # #
       # # # # #
      # # # # #
       # # # # #
      # # # # #
      """
output:     pattern = []
      for i in range(7):
          row = []
          for j in range(7):
              if (i + j) % 2 == 0:
                  row.append('#')
              else:
                  row.append(' ')
          pattern.append(''.join(row))
      return '\n'.join(pattern)