alternative to nested loops for large data set

[JonnyEnglish]

Hi, I've created some terribly slow code and I'd like to learn how I can improve it.

I want to turn the ownedcards dictionary of card id's and quantities into a list of card names and quantities.

ownedcards = {16: 2, 20: 139}

card_sections = [{'card_id': '16',
  'card_set': '1000',
  'fully_upgraded': '',
  'fusion_level': '0',
  'level': '1',
  'name': 'Terminator-1',
  'rarity': '2',
  'sp_value': '5'},
 {'card_id': '20',
  'card_set': '1000',
  'fully_upgraded': '',
  'fusion_level': '',
  'level': '3',
  'name': 'Benediction-3',
  'rarity': '4',
  'sp_value': '60'}]


card_names = []
for (card_id, qty) in ownedcards.items():
    for key in card_sections:
        if card_id == key['card_id']:
            card_names.append(key['name'] + ' #' + str(qty))


card_names outputs:

 ['Terminator-1 #2',
 'Benediction-3 #139']

card_sections is a list of 46750 dicts and the ownedcards dict can be 1000+ elements long so the above solution is really slow.

any advice would be appreciated

[Gribouillis]

You could start by grouping the card sections by their card_id. There are several ways to do that, here is one

from operator import itemgetter
import itertools

dic = {int(key): list(group) for key, group in itertools.groupby(
            sorted(card_sections, key=itemgetter('card_id')), key=itemgetter('card_id')))}

card_names = []
for card_id, qty in owned_cards.items():
    for sections in dic.get(card_id, []):
        card_names.extend('{}#{}'.format(s['name'], qty) for s in sections)

Alternately you could use more_itertools.bucket() if you have this module. Also note that in Python, 20 != '20'

[JonnyEnglish]

Great, thanks. Thats an interesting solution, I'll have to spend some time trying wrap my head around it.