def isvalid_sudoku(board):
    """
    Verifies that the board complies with the following conditions:

    -Each row must contain the digits 1-9 without repetition.
    -Each column must contain the digits 1-9 without repetition.
    -Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 
    without repetition
    
    Args:
        board (List[List[int]]): 9 x 9 sudoku grid with 0s or
        None at empty locations.
    """
    if not board or len(board) != 9 or not all(len(row) == 9 for row in board):
        return False

    #This can be simplified to use only one set, but it would hurt readability
    row = set()
    blocks = set()
    col = set()
    for i, r in enumerate(board):
        for j, num in enumerate(r):
            if (num, j) in col or (i, num) in row \
                or (num, i//3, j//3) in blocks:
                return False
            if num:
                col.add((num, j))
                row.add((i, num))
                blocks.add((num, i//3, j//3))
    
    return True