def build_report(config, trello):
reporter = Reporter()
for list_spec in config["lists"]:
trello_list = trello.list(list_spec["listId"])
old_cards = [
card for card in trello_list["cards"]
if older_than(card["dateLastActivity"], list_spec["timeDelta"])
]
if not old_cards:
continue
reporter.add_section(trello_list["name"],
[card["name"] for card in old_cards])
if not reporter.sections:
return None
return reporter.format(config["heading"])
