For the isValid Function, can't you just put it like this instead of having a for loop in it?

  def isValid(self, board, row, col, num):
    '''return True if Valid and False if not valid'''
    ### NEW VERSION ### - this passes the tests
    # Check if in ROW
    if board[row][:] == num: return False
    # Check if in COL
    if board[:][col] == num: return False
    # Check if in 3 x 3 GRID
    if (board[(row//3)*3 + row//3][(col//3)*3 + col%3] == num):
        return False
    return True
   
   ### ORIGINAL VERSION ### 
    for x in range(9):
    # Check if in ROW
      if board[row][x] == num: return False
      # Check if in COL
      if board[x][col] == num: return False
      # Check if in 3 x 3 GRID
      if (board[(row//3)*3 + x//3][(col//3)*3 + x%3] == num):
         return False
    return True