tzdata v0.1.6 → Overview → Tzdata

Tzdata

Summary
Functions

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

The database files from IANA are text files. Tzdata ships with a copy of the newest files. The dl_latest_data.sh script downloads the newest files. When a new version of the database is released from IANA you can run that script and recompile this library. Then the library will use the newest version of the database.

Or you can get an updated version of this tzdata Elixir library where the updated database is included.

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.

There are also functions for leap seconds. In the Tzdata.TableData module, data from the table that matches countries with time zones is available.

Summary↑

canonical_zone?(name)	Takes the name of a zone. Returns true if zone exists and is canonical. Otherwise 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
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
leap_seconds_with_tai_diff()	Get a list of maps with known leap seconds and the difference between UTC and the TAI in seconds
links()	Returns a map of links. Also known as aliases
periods(zone_name)	Returns a list of periods for the `zone_name` provided as an argument
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`
tzdata_version()	Returns tzdata release version as a string
zone_alias?(name)	Takes the name of a zone. Returns true if zone exists and is an alias. Otherwise 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 zone exists. Otherwise false
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

Functions

canonical_zone?(name)

(function) # ↑

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()

(function) # ↑

Like zone_list, but excludes aliases for zones.

leap_second_data_valid_until()

(function) # ↑

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()

(function) # ↑

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.

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()

(function) # ↑

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

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()

(function) # ↑

Returns a map of links. Also known as aliases.

iex> Tzdata.links["Europe/Jersey"]
"Europe/London"

periods(zone_name)

(function) # ↑

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: 59989766400, utc: 59989767284, wall: 59989766400},
  utc_off: -884, zone_abbr: "LMT"}]

periods_for_time(zone_name, time_point, time_type)

(function) # ↑

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()

(function) # ↑

Returns tzdata release version as a string.

Example:

Tzdata.tzdata_version
"2014i"

zone_alias?(name)

(function) # ↑

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()

(function) # ↑

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)

(function) # ↑

Takes the name of a zone. Returns true 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()

(function) # ↑

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

zone_lists_grouped()

(function) # ↑

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.