path.py

def neighbors(row, col, rows, cols):
    n = []
    for i, j in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
        if 0 <= col + i and col + i < cols and 0 <= row + j and row + j < rows:
            n.append((row + j, col + i))
                
    return n


def get_number_of_reachable_fields(grid, rows, columns, start_row, start_column):
    checked = set()
    to_search = set()
    reachable = set()

    to_search.add((start_row, start_column))

    # do a breadth first search
    while len(to_search) > 0:
        current = to_search.pop()
        checked.add(current)
        row, col = current
        # print current

        print row, col, neighbors(row, col, rows, columns)
        for nrow, ncol in neighbors(row, col, rows, columns):
            if grid[nrow][ncol] and (nrow, ncol) not in checked:
                reachable.add((nrow, ncol))
                to_search.add((nrow, ncol))

    print reachable
    return len([pair for pair in reachable if pair[0] == rows - 1])

Breadth First Search