Datetime conversion

Time math done by hand is where quiet mistakes come from: milliseconds read as seconds, a timezone offset applied the wrong way, DST ignored, a leap year forgotten. The bundled script removes all of that guesswork — run it and report what it says instead of computing in your head.

Usage

python3 scripts/dtconv.py [INPUT ...] [-z TZ] [--in-tz TZ] [-f FORMAT] [-u UNIT] [--add DELTA] [--diff OTHER] [--json]

Path is relative to this skill directory; use the absolute path when running from elsewhere. Standard library only. Python 3.9+ gets everything; on 3.7/3.8 the single casualty is IANA zone names (Asia/Shanghai), because zoneinfo does not exist there — the script says so and points at UTC / local / +08:00, and every other feature keeps working. Same story if zoneinfo exists but the tz database is missing (minimal containers, Windows): the error names the fix (pip install tzdata).

With no -f, the script prints a full report (epoch seconds and millis, UTC, local wall clock, ISO 8601, RFC 2822, weekday/ISO week/day-of-year, and a human "2 days ago"). When the user asked for one specific thing, pass -f and give them that single value.

• -z, --tz — output timezone: Asia/Shanghai, UTC, +08:00, local (default local)
• --in-tz — timezone assumed for input that has no offset (default local). Epoch numbers are absolute instants, so this does not affect them.
• -f, --format — named format or any strftime pattern. Named: iso, rfc3339, rfc2822, http, unix, unix_ms, unix_us, unix_ns, date, time, datetime, sql, compact, cn
• -u, --unit — force s|ms|us|ns for numeric input instead of auto-detecting, or excel to read spreadsheet serial numbers (45900 → 2025-08-31)
• --add — shift the result: +3d, -2h30m, 1 month, 1年2个月
• --diff — duration from input to another moment
• --json — machine-readable output, useful when feeding another script

Multiple inputs are converted in one call, one line of output each — prefer that over looping the script. For a whole column or file, pass the values as arguments (xargs works well) or use --json and post-process; a one-off sed/awk on date strings tends to break on the rows that do not match the shape you assumed.

Examples

# timestamp -> readable, in Beijing time
python3 scripts/dtconv.py 1735689600 -z Asia/Shanghai

# datetime string -> epoch millis, input understood as Beijing time
python3 scripts/dtconv.py "2026-08-26 15:30" --in-tz Asia/Shanghai -f unix_ms

# timezone hop, keeping only the wall clock
python3 scripts/dtconv.py "2026-08-26T07:30:00Z" -z America/New_York -f datetime

# natural language, several at once
python3 scripts/dtconv.py "3 days ago" "下周一 09:00" "明天下午3点" -f datetime

# arithmetic and durations
python3 scripts/dtconv.py now --add=-2h30m -f iso
python3 scripts/dtconv.py "2026-01-01" --diff "2026-12-25"

Input it understands

• Epoch numbers, unit inferred from magnitude: seconds, millis, micros, nanos; floats fine
• ISO 8601 / RFC 3339 in any shape: 2026-08-26T07:30:00Z, +08:00 or +0800 offsets, ISO basic format 20260826T073000, nanosecond fractions from Go/Java logs (digits below microsecond precision are dropped — datetime cannot hold them)
• RFC 2822 / HTTP dates (Wed, 01 Jan 2025 08:00:00 +0800)
• Common patterns: 2026-08-26 15:30:00, 2026/08/26, 20260826, 202608261530, 2026年8月26日, Aug 26 2026, bare 15:30 (means today)
• Relative phrases: now, today, tomorrow, yesterday, 前天/后天/大后天, 3 days ago, in 2 hours, 2天前, 3小时后, next friday, last monday, 下周一, 上个月, 明年, optionally with a time (tomorrow 9:30am, 明天下午3点)
• Spreadsheet serial numbers with -u excel (they look like plain integers, so this one is opt-in rather than auto-detected)

Not covered: cron expressions, business-day/holiday calendars, and Windows FILETIME. Say so rather than improvising if one of those comes up.

Things worth knowing before you answer

Naive input (no offset in the string) is interpreted in --in-tz, which defaults to the machine's local zone. When the user's data comes from a server in another zone, say so and pass --in-tz explicitly — this is the most common source of an off-by-N-hours answer.

An 8-digit number like 20260826 is read as a compact date, not a 1970s epoch, because that is almost always what it is. Pass -u s when you really do mean the epoch. If you are unsure which the user meant, the report line parsed as ... tells you what happened — quote it when the input was ambiguous.

01/02/2026 is genuinely ambiguous. The script assumes M/D/Y and prints a note with the D/M/Y reading; surface that note rather than silently picking one.

In --add, m means minutes and mo/月 means months. Month and year steps clamp the day, so Jan 31 + 1 month is Feb 28. Timezone conversion goes through the IANA database, so DST is handled — if a result looks an hour off around a DST boundary, it is probably right.

When the answer hinges on a timezone, include it in your reply (2025-01-01 08:00:00 +0800). A time without its zone is the kind of value that gets copied into a bug.