Simple sudoku puzzle solver python -

i'm trying write simple sudoku solver in python. basic concept sudoku puzzle partially filled in , unsolved cells indicated zeros. cell denoted 0 can solved @ stage of puzzle. if first cell 0, means values in row, column , 3x3 subgrid ensure there can 1 possible value cell. here code, seem stuck because output displays more 1 possibility. algorithm wrong?

def solveone (array, posr, posc):  possible = ['1','2','3','4','5','6','7','8','9']  col in range (9):     if array[posr][col] in possible:         possible.remove(array[posr][col])   row in range (9):     if array[row][posc] in possible:         possible.remove(array[row][posc])  row in range(posr, posr+3):     col in range (posc, posc+3):         if array[row::][col::] in possible:             possible.remove(array[row][col])  print (possible) return possible  grid = [["" _ in range(9)] _ in range(9)] #define 9x9 2-dimensional list  row in range(9):     aline = input() #prompt user enter 1 line of characters     col in range(9):         grid[row][col] = aline[col:col+1] #assign every character in line position in 2-d array  row in range(9):     col in range (9):         if grid[row][col] == '0':             r = row             c = col             newv = solveone (grid,r,c)             grid[row][col] = newv  print() in range (9):     k in range(9):         print(grid[i][k], end = "")     print() 

there several mistakes:

for row in range(posr, posr+3):     col in range (posc, posc+3):         if array[row::][col::] in possible:             possible.remove(array[row][col]) 

will not want do. better try (for python 2.7 - beware of div operation not doing float divison integer division):

block = ((posr/3)*3,(posc/3)*3) # top left cell of 3x3 block row in range(block[0], block[0]+3):     col in range (block[1], block[1]+3):         if array[row][col] in possible:             possible.remove(array[row][col]) 

so works better. doing

for row in range(9):     col in range (9):         if grid[row][col] == '0':             r = row             c = col             newv = solveone (grid,r,c)             grid[row][col] = newv 

you go through sudoku once. it's neccessary solve sudoku in more 1 step through - think that.

and have aware not every sudoku has unique solution. think solving empty sudoku - can pretty "do want".