Quick solution to sudoku checker. Does NOT check if board is correctly completable, only if it's currently correct.

sudoku.py

# Check nums for rows, columns and blocks  
def check(nums):
    num_dict = {}
    # assume nums is a list of integers
    # placeholder for empty is None
    for num in nums:
        if not num:
            continue
        if num in num_dict:
            return false
        else:
            num_dict[num] = false

# Check rows for board[i][j] (2d array)
def row_check(board):
    for row in board:
        if not check(row):
            return false
    return true

# Check columns for board
def column_check(board):
    for column in range(9):
        #column is int
        if not check([ row[column] for row in board ]):
            return false
    return true

# Check 3x3 blocks, index(0) by block_row, block_column
def block_check(board, block_row, block_col):
    # accumulate list
    #row is int
    nums = []
    for row in range(3 * block_row, 3 * block_row + 3):
        for column in range(3 * block_col, 3 * block_col + 3):
            nums.append(board[row][column])
        if not check(nums):
            return false
    
    return true

def check_board(board):
    if not row_check(board):
        return false
    
    if not column_check(board:
        return false
    
    for block_row in range(0,3):
        for block_col in range(0,3):
            if not block_check(board):
                return false
    
    return true