How do you iterate over a list of class objects in Python

Question

I'm attempting to iterate over a list of class objects/module objects to check collision and this error is thrown:

  File "C:/Users/travi/PycharmProjects/game/main.py", line 81, in <module>
if collision.collision1.is_collision(player.player1.vel, player.player1.x1, player.player1.x2, player.player1.y1, player.player1.y2, environmentVector[i].x1, environmentVector[i].x2, environmentVector[i].y1, environmentVector[i].y2):
TypeError: list indices must be integers or slices, not environment

heres the code (from main.py)

    for i in environmentVector:
        if collision.collision1.is_collision(player.player1.vel, player.player1.x1, player.player1.x2, player.player1.y1, player.player1.y2, environmentVector[i].x1, environmentVector[i].x2, environmentVector[i].y1, environmentVector[i].y2):
            print("collision")

environment.py:

import pygame

class environment():
    def __init__(self, x, y, width, height):
        self.x = x
        self.y = y
        self.x1 = x - 16
        self.x2 = x + 16
        self.y1 = y - 16
        self.y2 = y + 16

collision.py:

import pygame
import player
import enemy
import environment

class collision():
    def __init__(self):
        self.collision = False

    def is_collision(self, moveSpeed, x1, x2, y1, y2, X1, X2, Y1, Y2):
        if (((x2 + moveSpeed >= X1) and (x2 <= X2)) and (((y2 >= Y1) and (y2 <= Y2)) or ((y1 <= Y2) and (y1 >= Y1)))) or (((x1 - moveSpeed <= X2) and (x1 >= X1)) and (((y2 >= Y1) and (y2 <= Y2)) or ((y1 <= Y2) and (y1 >= Y1)))):
            return True
        else:
            return False

Python loops are for-each loops. In every iteration, i is the environment object itself, not a counter. — Daniel Roseman
– Daniel Roseman, Commented Nov 26, 2018 at 20:30

Aykhan Hagverdili · Accepted Answer · 2018-11-26 20:54:28Z

Python for loops are "for-each" type loops, unlike the traditional for loops in C and some other languages. In every iteration, loop variable (i in your case) is the next element in the container. Assuming vec is an std::vector<int> type, this in C++:

for (size_t i = 0; i != vec.size(); ++i){
    std::cout << vec[i] << std::endl;
}

Is roughly the equivalent of this in Python (lst is assumed to be a list object):

for i in lst:
    print(i)

As you can see i is the element itself, not its index.

Having said that, this is how your for loop could be fixed:

for i in environmentVector:
    if collision.collision1.is_collision(player.player1.vel, player.player1.x1, player.player1.x2, player.player1.y1, player.player1.y2, i.x1, i.x2, i.y1, i.y2):
        print("collision")

Notice that I replaced environmentVector[i]s with just is.

If you absolutely need indexes, you may use enumerate:
(lst is again assumed to be list object):

for indx, obj in enumerate(lst):
    print(indx, obj)

Here, in every iteration, you'll get the index assigned to indx and the object itself assigned to obj

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