Question

I’ve been completely stumped on this one:

I have the following python code:

def remove(self, widgets):
    for widget in widgets:
        widget_found = False
        for widget_sig in self.widgets:
            if widget_sig.id == widget:
                #remove all objects from selected widget
                widget_found = True
                to_remove = widget_sig.objs
                for obj in to_remove:
                    #objs are all intances of oo_canvas classes
                    obj.destroy()
                    self._build(widget, obj)
        if not widget_found:
            #if we iterated through the entire list and still couldn't find anything
            raise mockingbird_errs.InternalMockingbirdError("The requested widget was not registered with this builder: "+str(widget))

This should be pretty straight forward. The thing is, it never iterates through to_remove correctly. For some reason, it skips every other element. Even more baffling, is if I have it print the length of to_remove before and after the for loop, it prints 254 and 127. Huh? As far as I know, iterating through a list does not involve deleting every other element.

Am I missing something straightforward? What on earth is going on?

Answer 1

… it skips every other element.

That’s because you keep deleting them, shortening the list by 1. And then you move on to the next index. Either work backwards, or iterate over a copy of the list.