for team, scores in NL_East.items():
    runs_scored = float(scores[0])
runs_allowed = float(scores[1])
win_percentage = round(runs_scored ** 2 / (runs_scored ** 2 + runs_allowed **
    2) * 1000)
print('%s: %.1f%%' % (team, win_percentage))
Перебор ключевых значений словаря, соответствующих списку в Python