lesson completed

from collections import defaultdict

engagemnt_by_account = defaultdict(list)
for engagement_record in paid_engagement_in_first_week:
	account_key = engagement_record['account_key']
	engagement_by_account[account_key].append(engagement_record)

total_minutes_by_account = {}

for account_key, engegement_for_student in engagement_by_account.items():
	total_minutes = 0
	for engagement_record in engagement_for_student:
		total_minutes += engagement_record['total_minutes_visited']
	total_minutes_by_account[account_key] = total_minutes

total_minutes = total_minutes_by_account.values()

import numpy as np