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Code reviewMediumcr-g472
Subject Unnecessary allocationLevel Mid–Senior~20 minCommon in Code quality & review interviewsIndustries Software development

Question

Review this Python aggregation over event records.

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix — specific and kind.

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Code to reviewpython
from collections import defaultdict def bucket_by_user(events):    buckets = defaultdict(list)    seen_users = set()    for ev in events:        # only count a user the first time we see them        if ev.user_id not in buckets:            seen_users.add(ev.user_id)        buckets[ev.user_id].append(ev)    return buckets, seen_users
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