Question

This check for if some points are inside a rectangle, and whenever it’s run it slows my program down a lot. How can we change it to make it more efficient?

def draw_grid(self, box):
    for element in self.map_layout.all_map_objects:
        if element not in self.build_grid and box.area.collidepoint(element.checkpoint):
            self.build_grid.append(element)
        elif not box.area.collidepoint(element.checkpoint):
            if element in self.build_grid:
                self.build_grid.remove(element)

Answer 1

One change which is trivial to make is to store the result of box.area.collidepoint:

def draw_grid(self, box):
    for element in self.map_layout.all_map_objects:
        collidepoint = box.area.collidepoint(element.checkpoint)
        if element not in self.build_grid and collidepoint:
            self.build_grid.append(element)
        elif not collidepoint:
            if element in self.build_grid:
                self.build_grid.remove(element)

Other changes rely on the data structure that you need. For example, self.build_grid seems to be a list. __contains__ (in operator) on a list is an O(N) operation on average whereas if you could get by with a set, it would be O(1)!. The same thing goes with list.remove — Here you could use a try-except clause to remove one O(N) operation from the tight loop which might help if the element is usually in the list:

        elif not collidepoint:
            try:
                self.build_grid.remove(element)
            except ValueError:
                pass