Question

I have this code that creates a matrix filled with zeros. I want to replace some of the zeros with a “sign” which is given when creating a snake object. I then want to replace the zeros in the matrix with my sign without increasing the total amount of elements in the matrix.

With my “growth” function in the snake class I want to make sure that only zeros is overwritten but I get the error:

ValueError: (1, 4) is not in list 

When I’m sure that position actually do exist! The error code is different each time I run the program since the cordinates are generated on random. Here’s my code:

class field:
 def __init__(self):

    self.table= [ [ "0" for i in range(10) ] for j in range(10) ]

  def printfield(self):
     for row in self.table:
            print (row)


Class snake:

  def __init__(self,sign):
    self.sign = sign
    self.x = random.randint(1,9) 
    self.y = random.randint(1,9)    

    field.table[self.x][self.y] = sign


  def growth(self, list, index, element):
    if list[index] != 0:
        return False
    else:
        field.table[self.x-v*b][self.y-v*c] = element


  def increase(self,p,b,c):                                               

        for v in range(p+1):
                self.growth(field.table,field.table.index((self.x-v*b,self.y-v*c)), self.sign) 

Answer 1

You’re confusing your indices in the two-dimensional list with values in the list. The statement

field.table.index((self.x-v*b, self.y-v*c))

looks for a value of (in your given error case) (1, 4) inside of the list field.table, which is of course not there. What you probably want is accessing field.table[1][4]. You could just pass the tuple as a variable to growth and use its elements as indices for the list, or pass field.table[self.x-v*b] as the list to growth and self.y-v*c as the index to access on that list.

Also, you are filling the list with "0"s but checking against 0 inside your growth function.