title: Replace an element in a 2d list
body: <p>I continue to make my sudoku solver but I have a problem with my 2d list.</p>
  
  <p>My sudoku file txt looks like this : </p>
  
  <pre><code>..3 ... ...
  etc...
  </code></pre>
  
  <p>So here, right now, with this function :</p>
  
  <pre><code>def grid_index(grid, value):
      for i, row in enumerate(grid):
          for j, cell in enumerate(row):
               if cell == value:
                  return i, j
      return -1, -1
  print("Coords:",grid_index(sudoku, "."))
  </code></pre>
  
  <p>I found the first empty element who need to be change. The output is (0,0).</p>
  
  <p>Now, my point is to replace the element "." by 1 (for example) with the coordinates.</p>
  
  <p>My function to change is :</p>
  
  <pre><code>def solve_next_unsolved(sudoku):
      coords = grid_index(sudoku, ".") # so here i get coordinate to the point element
      number_to_input = 1
  </code></pre>
  
  <p>Should I get the element with coordinates? How can I change the element found by my <code>grid_index()</code> function with <code>1</code>?</p>