Sudoku solver in python with backtracking : <p>I saw a few sudoku solvers implementations ,but I cant figure out the problem in my code. I have a function sudokusolver which becomes sudoku Board and must return solved sudoku board.</p>

<pre><code>def sudokutest(s,i,j,z):
    # z is the number
    isiValid = np.logical_or((i+1&lt;1),(i+1&gt;9));
    isjValid = np.logical_or((j+1&lt;1),(j+1&gt;9));
    iszValid = np.logical_or((z&lt;1),(z&gt;9));
    if s.shape!=(9,9):
        raise(Exception("Sudokumatrix not valid"));
    if isiValid:
        raise(Exception("i not valid"));
    if isjValid:
        raise(Exception("j not valid"));
    if iszValid:
        raise(Exception("z not valid"));

    if(s[i,j]!=0):
        return False;

    for ii in range(0,9):
        if(s[ii,j]==z):
            return False;

    for jj in range(0,9):
        if(s[i,jj]==z):
            return False;

    row = int(i/3) * 3;
    col = int(j/3) * 3;
    for ii in range(0,3):
        for jj in range(0,3):
            if(s[ii+row,jj+col]==z):
                return False;

    return True;

def possibleNums(s , i ,j):
    l = [];
    ind = 0;
    for k in range(1,10):
        if sudokutest(s,i,j,k):
            l.insert(ind,k);
            ind+=1;
    return l;

def sudokusolver(S):
    zeroFound = 0;
    for i in range(0,9):
        for j in range(0,9):
            if(S[i,j]==0):
                zeroFound=1;
                break;
        if(zeroFound==1):
            break;
    if(zeroFound==0):
          return S;

    x = possibleNums(S,i,j);
    for k in range(len(x)):
        S[i,j]=x[k];
        sudokusolver(S);
    S[i,j] = 0;

    return S;
</code></pre>

<p>sudokutest and possibleNums are correct , only sudokusolver give a RecursionError</p>
