sorted(range(len(a)), key=lambda i: a[i])[-2:]
or
sorted(range(len(a)), key=lambda i: a[i], reverse=True)[:2]
or
import operator
zip(*sorted(enumerate(a), key=operator.itemgetter(1)))[0][-2:]
or (for long lists), consider using heapq.nlargest
zip(*heapq.nlargest(2, enumerate(a), key=operator.itemgetter(1)))[0]
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