python function returns None even if the code works properly

Question

Here is a solve function which solves a sudoku puzzle:

def solve(grid):
    for y in range(9):
        for x in range(9):
            if grid[y][x]==0:
                for n in range(1,10):
                    if possible(grid,y,x,n):
                        grid[y][x]=n
                        solve(grid)
                        grid[y][x]=0
                return
    print(np.matrix(grid))
    return grid

When solve function is called, it takes a matrix 9*9 sudoku puzzle and prints the solved puzzle.

The function works properly and the puzzle gets printed the right way. But instead of printing the puzzle I want the function to return the grid matrix and return in a variable like this:

solved_grid=solve(grid)

Instead of returning the grid the solve function returns None.

Kindly advise. Thanks in advance

You return `None` if `grid[y][x]==0`, which is in the first iteration of the first two `for` loops. — Guy, Mar 11 '20 at 09:50
^--- This and shouldn't your recursive call be `grid = solve(grid)` ? — Cid, Mar 11 '20 at 09:51
Does this answer your question? [I expect 'True' but get 'None'](https://stackoverflow.com/questions/15210646/i-expect-true-but-get-none) — guidot, Mar 11 '20 at 10:11

score 0 · Answer 1 · answered Mar 11 '20 at 09:51

0

That is because after your third loop you have a return,which does not return anything,but also terminates the execution of the program.

answered Mar 11 '20 at 09:51

adhitya ganesh

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python function returns None even if the code works properly

1 Answers1