Dynamic Programming - Hotel Problem

BOTTOM = 0
RIGHT = 1

def min_steps(movement_cost, life):
    rows = len(movement_cost)
    cols = len(movement_cost[0])
    m = [[None for __ in range(cols)] for _ in range(rows)]
    decisions = [[None for __ in range(cols)] for _ in range(rows)]
    life = [[None for __ in range(cols)] for _ in range(rows)]
    m[rows-1][cols-1] = 0   # starting point
    life[rows-1][cols-1] = 4

    for i in range(rows-1, -1, -1):
        for j in range(cols-1, -1, -1):
            if i == rows-1 and j == cols-1:
                continue
            # The above code is in order not to make m[len1, len2] ---> inf
            m[i][j] = float('inf')
            if i < rows-1:
                value = m[i + 1][j] + movement_cost[i][j]
                if value < m[i][j]:
                    m[i][j] = value
                    life[i][j] = life[i+1][j] - life_cost[i][j]
                    # Ήρθα από το κάτω κουτί
                    decisions[i][j] = BOTTOM
            if j < cols-1:
                value = m[i][j + 1] + movement_cost[i][j]
                if value < m[i][j]:
                    m[i][j] = value
                    # Ήρθα από το δεξιά κουτί
                    decisions[i][j] = RIGHT
                    life[i][j] = life[i][j+1] - life_cost[i][j]
    return m[0][0], decisions, life

# Creating the map with river and rocks
movement_cost = [[1 for __ in range(7)] for _ in range(8)]
# river
movement_cost[3][0] = 3
movement_cost[3][2] = 3
movement_cost[3][3] = 3
movement_cost[3][4] = 3
movement_cost[2][3] = 3
movement_cost[2][4] = 3
movement_cost[0][4] = 3
movement_cost[2][6] = 3
# rocks
movement_cost[0][2] = 5
movement_cost[4][2] = 5
movement_cost[4][3] = 5
movement_cost[6][2] = 5
movement_cost[7][2] = 5
movement_cost[5][5] = 5

life_cost = [[0 for __ in range(7)] for _ in range(8)]
life_cost[1][0] = 2
life_cost[1][3] = 3
life_cost[3][3] = 3
life_cost[3][6] = 2
life_cost[5][1] = 3
life_cost[5][3] = 3

#trees
life_cost[4][0] = -2
life_cost[7][1] = -2


def get_decisions(decisions, life, i, j):
    describe_square = "("+str(i)+","+str(j)+")  Life: "+str(life[i][j])
    if decisions[i][j] is None:
        return describe_square
    if decisions[i][j]==BOTTOM:
        return get_decisions(decisions, life, i+1, j)+"\n-> "+describe_square
    if decisions[i][j]==RIGHT:
        return get_decisions(decisions, life, i, j+1)+"\n-> "+describe_square
    raise Exception("Shouldn't be called")



steps, decisions, life = min_steps(movement_cost, life_cost)
print(steps)
print(get_decisions(decisions, life, 0, 0))