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Visual Studio Code – Python – Finding Index of a 2D Array (or Nested List)

I am putting together a terminal-based RPG where the map is 2D. Presently, I am attempting to find the index of the player’s position, which I will later use to move said player either north/south/east/west (based on the player’s action).

Here is my issue: the only indexes/indices that are stored (or this code works for) are [0][0], [1][1], and [2][2]. The error I receive is with line 20 (ValueError: ‘P’ is not in list). What can I do to adjust/edit my code so that I can find the index of "P" in other spots, such as [0][2] or [2][3]?

—————————Code Below———————————

  • A sample world map as a 2D array

  • P represents the player’s position

  • F represents part of a forest/a forest biome

  • To represents a town

    world_map = [[" ", " ", "F", "To"],
             [" ", " ", "F", "F"],
             [" ", "P", "", "F"]]

  • This global variable stores the previous value of a given index before the player moves –> use later for when player moves

    current_position = " "

  • This function iterates through the larger list and then the smaller lists/arrays

    def go_east():

  for x in range(len(world_map)):

      for y in range(len(world_map[x])):

          print(world_map[x][y])

          if (world_map[x][y] == "P"):

              position_x = world_map[x].index("P")

              position_y = world_map[y].index("P")

              print(position_x, position_y)

              print(world_map[x][y].index("P"))

go_east()

As said before, when I move "P" to a position that does not coincide with double digits (i.e. [1][1]), I receive a ValueError in relation to position_y (‘P’ is not in list). Changing the position of "P" to most other positions gives me the same error.

I am using Python 3.11.4 and Visual Studio Code.

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2

Answers


  1. 0

    your problem lies in these rows:

    position_x = world_map[x].index("P")

position_y = world_map[y].index("P")

    you are looking for p in the same index, so unless x == y you can’t find it.
    moreover, you have already found the indices of x an y through the loops so you can change the above lines to:

    position_x = x

position_y = y

    or, if you prefer:

    position_x, position_y = x, y

    also, whether you set the value of P manually or generate it randomly, i would suggest to save it to a variable and the moment of generation and the the movement will be just adding or subtracting the values of x and y

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  2. 0

    You’re referring to some wrong positions by accessing world_map[x].index("P") and world_map[y].index("P") – these two does not do what you expect them to do.

    Since you’re iterating in the nested loop with known x and y value at each step, you should use these values when assigning the position:

    position_x = x
position_y = y

    or just use these values directly.

    I have simplified your code just a bit and added 3 simple examples showing that the code works (aka "test on the go with semi-random values"):

    WORLD_MAP_ORIGINAL = [[" ", " ", "F", "To"],
                      [" ", " ", "F", "F"],
                      [" ", "P", " ", "F"]]
              
WORLD_MAP_ONE_LINE = [[" ", " ", " ", " ", "P", " ", " ", " "]]

WORLD_MAP_TWO_DIMS = [["A", " ", " ", "F", "T", " ", "B", "C"],
                      ["A", " ", " ", "F", "T", " ", "B", "J"],
                      ["A", " ", " ", "F", "T", " ", "B", "R"],
                      ["A", " ", " ", "F", "T", "P", "B", "H"],
                      ["A", " ", " ", "F", "T", " ", "B", "Z"],]

def go_east(world_map):
    for x in range(len(world_map)):
        for y in range(len(world_map[x])):
            if (world_map[x][y] == "P"):
                print(f"x = {x}, y = {y}, value = {world_map[x][y]}")

go_east(WORLD_MAP_ORIGINAL) // prints x = 2, y = 1, value = P
go_east(WORLD_MAP_ONE_LINE) // prints x = 0, y = 4, value = P
go_east(WORLD_MAP_TWO_DIMS) // prints x = 3, y = 5, value = P
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