tzdata v0.5.12 Tzdata

The Tzdata module provides data from the IANA tz database. Also known as the Olson/Eggert database, zoneinfo, tzdata and other names.

A list of time zone names (e.g. America/Los_Angeles) are provided. As well as functions for finding out the UTC offset, abbreviation, standard offset (DST) for a specific point in time in a certain timezone.

Summary

Functions

Takes the name of a zone. Returns true if zone exists and is canonical. Otherwise false

Like zone_list, but excludes aliases for zones

The time when the leap second information returned from the other leap second related function expires. The date-time is in UTC

Get a list of known leap seconds. The leap seconds are datetime tuples representing the extra leap second to be inserted. The date-times are in UTC

Get a list of maps with known leap seconds and the difference between UTC and the TAI in seconds

Returns a map of links. Also known as aliases

Returns a list of periods for the zone_name provided as an argument

Get the periods that cover a certain point in time. Usually it will be a list with just one period. But in some cases it will be zero or two periods. For instance when going from summer to winter time (DST to standard time) there will be an overlap if time_type is :wall

Returns tzdata release version as a string

Takes the name of a zone. Returns true if zone exists and is an alias. Otherwise false

A list of aliases for zone names. For instance Europe/Jersey is an alias for Europe/London. Aliases are also known as linked zones

Takes the name of a zone. Returns true if zone exists. Otherwise false

zone_list provides a list of all the zone names that can be used with DateTime. This includes aliases

Returns a map with keys being group names and the values lists of time zone names. The group names mirror the file names used by the tzinfo database

Functions

canonical_zone?(name)

Takes the name of a zone. Returns true if zone exists and is canonical. Otherwise false.

iex> Tzdata.canonical_zone? "Europe/London"
true
iex> Tzdata.canonical_zone? "Europe/Jersey"
false
canonical_zone_list()

Like zone_list, but excludes aliases for zones.

leap_second_data_valid_until()

The time when the leap second information returned from the other leap second related function expires. The date-time is in UTC.

Example

Tzdata.leap_second_data_valid_until
{{2015, 12, 28}, {0, 0, 0}}
leap_seconds()

Get a list of known leap seconds. The leap seconds are datetime tuples representing the extra leap second to be inserted. The date-times are in UTC.

See also leap_seconds_with_tai_diff/1

Example

iex> Tzdata.leap_seconds |> Enum.take(3)
[{{1971, 12, 31}, {23, 59, 60}},
 {{1972,  6, 30}, {23, 59, 60}},
 {{1972, 12, 31}, {23, 59, 60}}]
leap_seconds_with_tai_diff()

Get a list of maps with known leap seconds and the difference between UTC and the TAI in seconds.

See also leap_seconds/1

Example

iex> Tzdata.leap_seconds_with_tai_diff |> Enum.take(3)
[%{date_time: {{1971, 12, 31}, {23, 59, 60}}, tai_diff: 10},
 %{date_time: {{1972,  6, 30}, {23, 59, 60}}, tai_diff: 11},
 %{date_time: {{1972, 12, 31}, {23, 59, 60}}, tai_diff: 12}]
links()

Returns a map of links. Also known as aliases.

iex> Tzdata.links["Europe/Jersey"]
"Europe/London"
periods(zone_name)

Returns a list of periods for the zone_name provided as an argument.

A period in this case is a period of time where the UTC offset and standard offset are in a certain way. When they change, for instance in spring when DST takes effect, a new period starts. For instance a period can begin in spring when winter time ends and summer time begins. The period lasts until DST ends.

If either the UTC or standard offset change for any reason, a new period begins. For instance instead of DST ending or beginning, a rule change that changes the UTC offset will also mean a new period.

The result is tagged with :ok if the zone_name is correct.

The from and until times can be :mix, :max or gregorian seconds.

Example

iex> Tzdata.periods("Europe/Madrid") |> elem(1) |> Enum.take(1)
[%{from: %{standard: :min, utc: :min, wall: :min}, std_off: 0,
  until: %{standard: 59989763760, utc: 59989764644, wall: 59989763760},
  utc_off: -884, zone_abbr: "LMT"}]
iex> Tzdata.periods("Not existing")
{:error, :not_found}
periods_for_time(zone_name, time_point, time_type)

Get the periods that cover a certain point in time. Usually it will be a list with just one period. But in some cases it will be zero or two periods. For instance when going from summer to winter time (DST to standard time) there will be an overlap if time_type is :wall.

zone_name should be a valid time zone name. The function zone_list/0 provides a valid list of valid zone names.

time_point is the point in time in gregorian seconds (see erlang calendar module documentation for more info on gregorian seconds).

Valid values for time_type is :utc, :wall or :standard.

Examples

# 63555753600 seconds is equivalent to {{2015, 1, 1}, {0, 0, 0}}
iex> Tzdata.periods_for_time("Asia/Tokyo", 63587289600, :wall)
[%{from: %{standard: 61589206800, utc: 61589174400, wall: 61589206800}, std_off: 0,
  until: %{standard: :max, utc: :max, wall: :max}, utc_off: 32400, zone_abbr: "JST"}]

# 63612960000 seconds is equivalent to 2015-10-25 02:40:00 and is an ambiguous
# wall time for the zone. So two possible periods will be returned.
iex> Tzdata.periods_for_time("Europe/Copenhagen", 63612960000, :wall)
[%{from: %{standard: 63594813600, utc: 63594810000, wall: 63594817200}, std_off: 3600,
        until: %{standard: 63612957600, utc: 63612954000, wall: 63612961200}, utc_off: 3600, zone_abbr: "CEST"},
      %{from: %{standard: 63612957600, utc: 63612954000, wall: 63612957600}, std_off: 0,
        until: %{standard: 63626263200, utc: 63626259600, wall: 63626263200}, utc_off: 3600, zone_abbr: "CET"}]

# 63594816000 seconds is equivalent to 2015-03-29 02:40:00 and is a
# non-existing wall time for the zone. It is spring and the clock skips that hour.
iex> Tzdata.periods_for_time("Europe/Copenhagen", 63594816000, :wall)
[]
tzdata_version()

Returns tzdata release version as a string.

Example:

Tzdata.tzdata_version
"2014i"
zone_alias?(name)

Takes the name of a zone. Returns true if zone exists and is an alias. Otherwise false.

iex> Tzdata.zone_alias? "Europe/Jersey"
true
iex> Tzdata.zone_alias? "Europe/London"
false
zone_alias_list()

A list of aliases for zone names. For instance Europe/Jersey is an alias for Europe/London. Aliases are also known as linked zones.

zone_exists?(name)

Takes the name of a zone. Returns true if zone exists. Otherwise false.

iex> Tzdata.zone_exists? "Pacific/Auckland"
true
iex> Tzdata.zone_exists? "America/Sao_Paulo"
true
iex> Tzdata.zone_exists? "Europe/Jersey"
true
zone_list()

zone_list provides a list of all the zone names that can be used with DateTime. This includes aliases.

zone_lists_grouped()

Returns a map with keys being group names and the values lists of time zone names. The group names mirror the file names used by the tzinfo database.