RosettaCode- Sudoku created by tapicella - https://repl.it/HzMK/82

RosettaCode- Sudoku.py

'''

http://rosettacode.org/wiki/Sudoku

'''
import copy 

square_ranges = {
  0: [0, 1, 2],
  1: [0, 1, 2],
  2: [0, 1, 2],
  3: [3, 4, 5],
  4: [3, 4, 5],
  5: [3, 4, 5],
  6: [6, 7, 8],
  7: [6, 7, 8],
  8: [6, 7, 8]
}

sumnums = sum([1, 2, 3, 4, 5, 6, 7, 8, 9])

def checkHoriz(sudoku, y):
  valid = [1, 2, 3, 4, 5, 6, 7, 8, 9]
  relatives = []
  for x in range(len(sudoku[y])):
    relatives.append((x, y))
    if sudoku[y][x]!= '': 
      try: valid.remove(sudoku[y][x])
      except:
        pass
  return valid, relatives

def checkVert(sudoku, x):
  valid = [1, 2, 3, 4, 5, 6, 7, 8, 9]
  relatives = []
  for y in range(len(sudoku)):
    relatives.append((x, y))
    if sudoku[y][x] != '': 
      try: valid.remove(sudoku[y][x])
      except:
        pass
  return valid, relatives 

def checkSquare(sudoku, coord):
  valid = [1, 2, 3, 4, 5, 6, 7, 8, 9]
  relatives = []
  xranges = square_ranges[coord[0]]
  yranges = square_ranges[coord[1]]
  for x in xranges:
    for y in yranges:
      relatives.append((x, y))
      if sudoku[y][x] != '':
        try: valid.remove(sudoku[y][x])
        except:
          pass
  return valid, relatives
  
def solve(sudoku):
  relationships = {}
  prevsudoku = []
  for y in range(len(sudoku)):
    for x in range(len(sudoku[y])):
      if sudoku[y][x]=='':
        valid_h, relatives_h = checkHoriz(sudoku, y)
        valid_v, relatives_v = checkVert(sudoku, x)
        valid_s, relatives_s = checkSquare(sudoku, (x, y))
        valid = list(set(valid_h) & set(valid_v) & set(valid_s))
        relatives = list(set(relatives_h+relatives_v+relatives_s))
        relationships[(x, y)] = {"valid" : valid, "relatives":relatives}
  
  while len(relationships.keys()) > 0:
    for k in relationships:
      k_valid = relationships[k]["valid"]
      if len(k_valid)==1:
        k_val = k_valid[0]
        sudoku[k[1]][k[0]] = k_val
        for k2 in relationships:
          if k in relationships[k2]["relatives"]:
            neighbor_found = relationships[k2]["relatives"]
            try:
              relationships[k2]["valid"].remove(k_val)
            except:
              pass
        relationships.pop(k)
        break;
    if prevsudoku == sudoku: 
      print("infinite loop")
      return False
    prevsudoku = copy.deepcopy(sudoku)
    print(sudoku)
      
      
sudoku =  [[5, 3, '', '', 7, '', '', '' ,''],
   [6, '', '', 1, 9, 5, '', '', ''],
   ['', 9, 8, '' ,'' ,'', '', 6, ''],
   [8, '', '', '', 6, '', '', '', 3],
   [4, '', '', 8, '', 3, '', '', 1],
   [7, '', '', '', 2, '', '', '', 6],
   ['', 6, '', '', '', '', 2, 8, ''],
   ['', '', '', 4, 1, 9, '', '', 5],
   ['', '', '', '', 8, '', '', 7, 9]]
   
solve(sudoku)