Why does this function print the result, but return none?

Question

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

This function prints the solved Sudoku, however print(solve(sudoku)) returns none. Why does the function return none if it can print(sudoku)?

Answer 1

def solve(sudoku):
    for y in range(9):
        for x in range(9):
            if sudoku[y][x] == 0:
                for n in range(1, 10): 
                    if possible(x, y, n):
                        sudoku[y][x] = n
                        solve(sudoku)
                        sudoku[y][x] = 0
                        
                return # this might be a problem
    print(np.matrix(sudoku))
    return sudoku

Answer 2

Your assumptions must be wrong.

If you are saying that print(solve(sudoku)) print None , then this must be what is happening.

The only way for that to happen is if the last return is from the third line from the bottom of your code.