how do i turn for loop iterator into a neat pythonic one line for loop

Question

I really love shrinking my code into as few lines as possible. I have the code below and I been trying to get it into one line, if anyone can advise, i would appreciate it.

        list_choices = {}
        if_changed = ''
        for i in obj:
            if if_changed!=i.area.region.id:
                if_changed = i.area.region.id
                list_choices.setdefault(if_changed, [])

            list_choices[if_changed].append([i.id, i.name])

Answer 1

list_choices = {}
for i in obj:
    list_choices.setdefault(i.area.region.id, []).append([i.id, i.name])

or, using list_choices = collections.defaultdict(list) the last line will be:

list_choices[i.area.region.id].append([i.id, i.name])

Answer 2

Not very clear what you want to do, so I'm guessing you want to group things in obj by their area.region.id and then add them to a dictionary:

import itertools

list_choices = {}
obj_by_region = itertools.groupby(obj, key=lambda x: x.area.region.id)
for region, elements in obj_by_region:
    list_choices[region] = [[el.id, el.name] for el in elements]