How to get try: except: working without going on infinitely

user_13309591 0
Viewed 63

So I have a 2d list, named tour:

tour = [ [3, 2, 1,], 
         [4, 7, 9,], 
         [5, 6, 8,], ]

I want my code to check through this list and see if a king (chess) can go through it normally. The code I made can be applicable on a N×N 2d list. What it does is that it starts on number 1, and checks all 9 spaces around it if there is a number 2, repeating the process till N×N. The problem is that when the number is at a side of the list the code gives an IndexError, to overcome this I made a try: except: IndexError but now when it gets to i = 6 it keeps on going infinitely

def in_list(number, listname):
    """
    this function detects where a certain number is in a 2d list and returns the index of 
    it
    """
    for i, sublist in enumerate(listname):
        if (number in sublist):
            return [i, sublist.index(number)]
        
    return -1
            

def is_king_tour_3by3(tour):
    """
    this function checks for all 9 areas around this number and if it's an IndexError
    i.e. it's at the end of the list it ignores that case
    """
    start = in_list(1, tour)
    i = 2
    counter = len(tour) * len(tour)
    
    while True:
        counter -= 1
        print(i)
        print(start)
        try:
            if(tour[start[0]][start[1] - 1] == i): #starting from checking the number on the left and going counter-clockwise
                i += 1
                start[1] -= 1
            elif(tour[start[0] + 1][start[1] - 1] == i):    
                i += 1
                start[0] += 1
                start[1] -= 1
            elif(tour[start[0] + 1][start[1]] == i):
                i += 1
                start[0] += 1
            elif(tour[start[0] + 1][start[1] + 1] == i):
                i += 1
                start[0] += 1
                start[1] += 1
            elif(tour[start[0]][start[1] + 1] == i):
                i += 1
                start[1] += 1
            elif(tour[start[0] - 1][start[1] + 1] == i):
                i += 1
                start[0] -= 1
                start[1] += 1
            elif(tour[start[0] - 1][start[1]] == i):
                i += 1
                start[0] -= 1
            elif(tour[start[0] - 1][start[1] - 1] == i):
                i += 1
                start[0] -= 1
                start[1] -= 1
        except IndexError:
            pass
        
        if(i == (len(tour) * len(tour))):
            return True
            break
        elif(counter == 0):
            return False
            break
try-except list python
1 Answers

By adding start[0] < len(tour)-1 and start[1] > 0 to the rows you can check that you are not outside the 2d list instead of using a try: except:. This code will solve it as long as start is > 0 and < len(tour) (if start[0] or start[1] is -1 or len(tour) it might fail):

def in_list(number, listname):
    """
    this function detects where a certain number is in a 2d list and returns the index of 
    it
    """
    for i, sublist in enumerate(listname):
        if (number in sublist):
            return [i, sublist.index(number)]
    
return -1
        

def is_king_tour_3by3(tour):
    """
    this function checks for all 9 areas around this number and if it's an IndexError
    i.e. it's at the end of the list it ignores that case
    """
    start = in_list(1, tour)
    i = 2
    counter = len(tour) * len(tour)
    
while True:
    counter -= 1
    print(i)
    print(start)
    if(start[1] > 0 and tour[start[0]][start[1] - 1] == i): #starting from checking the number on the left and going counter-clockwise
        i += 1
        start[1] -= 1
    elif(start[0] < len(tour)-1 and start[1] > 0 and tour[start[0] + 1][start[1] - 1] == i):    
        i += 1
        start[0] += 1
        start[1] -= 1
    elif(start[0] < len(tour)-1 and tour[start[0] + 1][start[1]] == i):
            i += 1
            start[0] += 1
    elif(start[0] < len(tour)-1 and start[1] < len(tour)-1 and tour[start[0] + 1][start[1] + 1] == i):
        i += 1
        start[0] += 1
        start[1] += 1
    elif(start[1] < len(tour)-1 and tour[start[0]][start[1] + 1] == i):
        i += 1
        start[1] += 1
    elif(start[0] > 0 and start[1] < len(tour)-1 and tour[start[0] - 1][start[1] + 1] == i):
        i += 1
        start[0] -= 1
        start[1] += 1
    elif(start[0] > 0 and tour[start[0] - 1][start[1]] == i):
        i += 1
        start[0] -= 1
    elif(start[0] > 0 and start[1] > 0 and tour[start[0] - 1][start[1] - 1] == i):
        i += 1
        start[0] -= 1
        start[1] -= 1
    
    if(i == (len(tour) * len(tour))):
        return True
        break
    elif(counter == 0):
        return False
        break

tour = [ [3, 2, 1,], 
         [4, 7, 9,], 
         [5, 6, 8,], ]
is_king_tour_3by3(tour)
user_38716390
Related