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Nine A.M. Somewhere — Python Bug Hunt

Inspired by the digest emails that arrive at 3 AM: "send at 9 AM" was implemented as 9 AM server time, for every user on the planet.

  • Language: Python
  • Layer: Backend
  • Difficulty: Easy
  • Concepts: Timezones, Scheduling
  • Modelled on: Lifecycle email
  • Visible tests: east-of-UTC users send earlier in UTC; west-of-UTC users send later in UTC
  • Reward: 50 XP for a complete fix

Briefing

Inspired by the digest emails that arrive at 3 AM: "send at 9 AM" was implemented as 9 AM server time, for every user on the planet.

digest.py converts each user's local send-hour to the UTC hour the scheduler runs on. Offsets are minutes east of UTC.

Bug report

BUG-9AM · Reported by: lifecycle marketing

send_hour_utc(local_hour, offset_minutes):

  • the UTC hour at which the user's wall clock reads local_hour
  • Mumbai (+330): 9 AM local -> 3 UTC
  • New York (-300): 9 AM local -> 14 UTC

Observed: the offset is ignored — everyone gets the digest at server 9 AM.

Logs

[digest] IST users report 2:30 PM delivery; PST users 1 AM

The code as shipped

src/mail/digest.py (editable)

# UTC hour at which to send a user's local-time digest.

def send_hour_utc(local_hour, offset_minutes):
    return local_hour

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