Reference · Dates

date.valid_zone

date.valid_zone(any) -> bool

What it does

Whether a value is a time zone: a name of the IANA database, a zone or a link, in any case ("Europe/Paris", "US/Pacific", "EST"), an offset as date.parse reads one ("+05:45", "+0530", "+05", up to +23:59), or "UTC". The server and the browser take the same zones and refuse the same names. A zone is among the commonest values a program takes from a person, and one that does not exist stops date.to_zone, so ask first, or guard it with ??.

Examples

print(date.valid_zone("Europe/Paris"))print(date.valid_zone("+05:45"))print(date.valid_zone("Mars/Base"))print(date.to_zone("2026-10-27T14:30:00Z", "Mars/Base") ?? "no such zone")

truetruefalseno such zone

Edge cases

• Names some systems keep beside the database are no zones, on either side: posixrules, Factory, Etc/Unknown, localtime, posix/... and right/....
• So are names the database dropped (US/Pacific-New, Canada/East-Saskatchewan, SystemV/...), Java's three-letter ids (PST), and any other name with a sign (+5, +0560, +24:00, a U+2212 minus).
• The server reads the system's time zone database, and a copy built into quillo for a name the system's leaves out, or where there is none (Windows, small containers); the browser asks its own (Intl). So EST, US/Pacific, Asia/Calcutta and EST5EDT, which Ubuntu 24.04 moved to a package of their own (tzdata-legacy), are zones on every machine.

print(["europe/paris", "US/Pacific", "EST", "+0530", "+05", "+23:59"] | map(date.valid_zone))print(["PST", "posixrules", "Factory", "right/UTC", "US/Pacific-New", "+5", "+24:00"] | map(date.valid_zone))print(date.from_ms(1793543400000, "+0530"), date.to_zone("2026-10-27T14:30:00Z", "europe/paris"))

[true, true, true, true, true, true][false, false, false, false, false, false, false]2026-11-01T20:00:00+05:30 2026-10-27T15:30:00+01:00

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