sudoku_grid.py

# Python 2
# simple sudoku scratchpad
#
# Sample grid load:
# =916354872 873629154 524718936 768935241 149287365 235461798 697842513 381576429 452193
# Solution to sample (687 in locations 7,9, 8,9, and 9,9):
# 796 898 997

grid = ['.'] * 81

def row_set (y):
    return set(grid[y*9: y*9+9]) - set('.')

def col_set (x):
    return set(grid[x: x+81: 9]) - set('.')

# Box #s 0..8 left-to-right and top-to-bottom
def box_set (n):
    return set([grid[y*9+x]
      for x in range((n % 3) * 3, (n % 3) * 3 + 3)
      for y in range(n // 3 * 3, n // 3 * 3 + 3)]) - set('.')

def format_row (y):
    return '|' + ''.join(grid[y*9: y*9+3]) + \
      '|' + ''.join(grid[y*9+3: y*9+6]) + \
      '|' + ''.join(grid[y*9+6: y*9+9]) + '|'

def print_grid ():
    print ' x123 456 789'
    print 'y+---+---+---+'
    for y in range(0, 9):
        print str(y+1) + format_row(y)
        if y % 3 == 2: print ' +---+---+---+'

def load_grid (digits):
    grid = ['.'] * 81
    for i in range(0, min(81, len(digits))):
    set_grid(i % 9, i // 9, digits[i])

def set_grid (x, y, digit):
    if '1' <= digit <= '9':
    box = y // 3 * 3 + x // 3
    if digit in col_set(x):
        print 'There is already a', digit, 'in column', x + 1
    elif digit in row_set(y):
        print 'There is already a', digit, 'in row', y + 1
    elif digit in box_set(box):
        print 'There is already a', digit, 'in box', box + 1
    else:
        grid[y * 9 + x] = digit
    else:
    grid[y * 9 + x] = '.'

print "Enter '= digit digit ...' to load the grid (0 or . for empty)."
print "Enter 'x y digit ...' to set specific grid squares."
while True:
    changes = list(raw_input('Load/change: ').replace(' ', ''))
    if len(changes) and changes[0] == '=':
    load_grid(changes[1:])
    else:
    while len(changes) > 2:
        set_grid(int(changes[0]) - 1, int(changes[1]) - 1, changes[2])
        changes = changes[3:]
    print_grid()
    if '.' not in grid:
    print 'Solved!'
    break