code: def cell_key_val_gen(iterable, shape, topleft=(0, 0)):
      
  
      top, left = topleft
  
      for __row, line in enumerate(iterable):
          row = top + __row
          if row >= shape[0]:
              break
  
          for __col, value in enumerate(line):
              col = left + __col
              if col >= shape[1]:
                  break
  
              yield row, col, value
docs: Generator of row, col, value tuple from iterable of iterables
  
      it: Iterable of iterables
      \tMatrix that shall be mapped on target grid
      shape: Tuple of Integer
      \tShape of target grid
      topleft: 2-tuple of Integer
      \tTop left cell for insertion of it