'Find the first uncovered element with value 0'

def __find_a_zero(self):

    row = (-1)
    col = (-1)
    i = 0
    n = self.n
    done = False
    while (not done):
        j = 0
        while True:
            if ((self.C[i][j] == 0) and (not self.row_covered[i]) and (not self.col_covered[j])):
                row = i
                col = j
                done = True
            j += 1
            if (j >= n):
                break
        i += 1
        if (i >= n):
            done = True
    return (row, col)
