TZInfo - Ruby Time Zone Library

TZInfo is a Ruby library that provides access to time zone data and allows times to be converted using time zone rules.

Data Sources

TZInfo requires a source of time zone data. There are two options:

1. A zoneinfo directory containing timezone definition files. These files are generated from the IANA Time Zone Database using the zic utility. Most Unix-like systems include a zoneinfo directory.
2. The TZInfo::Data library (the tzinfo-data gem). TZInfo::Data contains a set of Ruby modules that are also generated from the IANA Time Zone Database.

By default, TZInfo will attempt to use TZInfo::Data. If TZInfo::Data is not available (i.e. if require 'tzinfo/data' fails), then TZInfo will search for a zoneinfo directory instead (by checking the directories specified by TZInfo::DataSources::ZoneinfoDataSource.search_path in turn).

If no data source can be found, a TZInfo::DataSourceNotFound exception will be raised when TZInfo is used. Further information is available in the wiki to help resolve TZInfo::DataSourceNotFound errors.

The default data source selection can be overridden by calling TZInfo::DataSource.set.

Custom data sources can also be used. See the TZInfo::DataSource.set documentation for further details.

Installation

The TZInfo gem can be installed by running gem install tzinfo or by adding gem 'tzinfo' to your Gemfile and running bundle install.

To use the Ruby modules as the data source, TZInfo::Data will also need to be installed by running gem install tzinfo-data or by adding gem 'tzinfo-data' to your Gemfile.

IANA Time Zone Database

The data returned and used by TZInfo is sourced from the IANA Time Zone Database. The Theory and pragmatics of the tz code and data document gives details of how the data is organized and managed.

Example Usage

To use TZInfo, it must first be required with:

require 'tzinfo'

The TZInfo::Timezone class provides access to time zone data and methods for converting times.

The all_identifiers method returns a list of valid time zone identifiers:

identifiers = TZInfo::Timezone.all_identifiers
# => ["Africa/Adibdjan", "Africa/Accra", ..., "Zulu"]

A TZInfo::Timezone instance representing an individual time zone can be obtained with TZInfo::Timezone.get:

tz = TZInfo::Timezone.get('America/New_York')
# => #<TZInfo::DataTimezone: America/New_York>

A time can be converted to the local time of the time zone with to_local:

tz.to_local(Time.utc(2018, 2, 1, 12, 30, 0))
# => 2018-02-01 07:30:00 -0500
tz.to_local(Time.utc(2018, 7, 1, 12, 30, 0))
# => 2018-07-01 08:30:00 -0400
tz.to_local(Time.new(2018, 7, 1, 13, 30, 0, '+01:00'))
# => 2018-07-01 08:30:00 -0400

Local times with the appropriate offset for the time zone can be constructed with local_time:

tz.local_time(2018, 2, 1, 7, 30, 0)
# => 2018-02-01 07:30:00 -0500
tz.local_time(2018, 7, 1, 8, 30, 0)
# => 2018-07-01 08:30:00 -0400

Local times can be converted to UTC by using local_time and calling utc on the result:

tz.local_time(2018, 2, 1, 7, 30, 0).utc
# => 2018-02-01 12:30:00 UTC
tz.local_time(2018, 7, 1, 8, 30, 0).utc
# => 2018-07-01 12:30:00 UTC

The local_to_utc method can also be used to convert a time object to UTC. The offset of the time is ignored - it is treated as if it were a local time for the time zone:

tz.local_to_utc(Time.utc(2018, 2, 1, 7, 30, 0))
# => 2018-02-01 12:30:00 UTC
tz.local_to_utc(Time.new(2018, 2, 1, 7, 30, 0, '+01:00'))
# => 2018-02-01 12:30:00 UTC

Information about the time zone can be obtained from returned local times:

local_time = tz.to_local(Time.utc(2018, 2, 1, 12, 30, 0))
local_time.utc_offset  # => -18000
local_time.dst?        # => false
local_time.zone        # => "EST"

local_time = tz.to_local(Time.utc(2018, 7, 1, 12, 30, 0))
local_time.utc_offset  # => -14400
local_time.dst?        # => true
local_time.zone        # => "EDT"

Time zone information can be included when formatting times with strftime using the %z and %Z directives:

tz.to_local(Time.utc(2018, 2, 1, 12, 30, 0)).strftime('%Y-%m-%d %H:%M:%S %z %Z')
# => "2018-02-01 07:30:00 -0500 EST"
tz.to_local(Time.utc(2018, 7, 1, 12, 30, 0)).strftime('%Y-%m-%d %H:%M:%S %z %Z')
# => "2018-07-01 08:30:00 -0400 EDT"

The period_for method can be used to obtain information about the observed time zone information at a particular time as a TZInfo::TimezonePeriod object:

period = tz.period_for(Time.utc(2018, 7, 1, 12, 30, 0))
period.base_utc_offset          # => -18000
period.std_offset               # => 3600
period.observed_utc_offset      # => -14400
period.abbreviation             # => "EDT"
period.dst?                     # => true
period.local_starts_at.to_time  # => 2018-03-11 03:00:00 -0400
period.local_ends_at.to_time    # => 2018-11-04 02:00:00 -0400

A list of transitions between periods where different rules are observed can be obtained with the transitions_up_to method. The result is returned as an Array of TZInfo::TimezoneTransition objects:

transitions = tz.transitions_up_to(Time.utc(2019, 1, 1), Time.utc(2017, 1, 1))
transitions.map do |t|
  [t.local_end_at.to_time, t.offset.observed_utc_offset, t.offset.abbreviation]
end
# => [[2017-03-12 02:00:00 -0500, -14400, "EDT"],
#     [2017-11-05 02:00:00 -0400, -18000, "EST"],
#     [2018-03-11 02:00:00 -0500, -14400, "EDT"],
#     [2018-11-04 02:00:00 -0400, -18000, "EST"]]

A list of the unique offsets used by a time zone can be obtained with the offsets_up_to method. The result is returned as an Array of TZInfo::TimezoneOffset objects:

offsets = tz.offsets_up_to(Time.utc(2019, 1, 1))
offsets.map {|o| [o.observed_utc_offset, o.abbreviation] }
# => [[-17762, "LMT"],
#     [-18000, "EST"],
#     [-14400, "EDT"],
#     [-14400, "EWT"],
#     [-14400, "EPT"]]

All TZInfo::Timezone methods that accept a time as a parameter can be used with either instances of Time, DateTime or TZInfo::Timestamp. Arbitrary Time-like objects that respond to both to_i and subsec and optionally utc_offset will be treated as if they are instances of Time.

TZInfo::Timezone methods that both accept and return times will return an object with a type matching that of the parameter (actually a TZInfo::TimeWithOffset, TZInfo::DateTimeWithOffset or TZInfo::TimestampWithOffset subclass when returning a local time):

tz.to_local(Time.utc(2018, 7, 1, 12, 30, 0))
# => 2018-07-01 08:30:00 -0400
tz.to_local(DateTime.new(2018, 7, 1, 12, 30, 0))
# => #<TZInfo::DateTimeWithOffset: 2018-07-01T08:30:00-04:00 ((2458301j,45000s,0n),-14400s,2299161j)>
tz.to_local(TZInfo::Timestamp.create(2018, 7, 1, 12, 30, 0, 0, :utc))
# => #<TZInfo::TimestampWithOffset: @value=1530448200, @sub_second=0, @utc_offset=-14400, @utc=false>

In addition to local_time, which returns Time instances, the local_datetime and local_timestamp methods can be used to construct local DateTime and TZInfo::Timestamp instances with the appropriate offset:

tz.local_time(2018, 2, 1, 7, 30, 0)
# => 2018-02-01 07:30:00 -0500
tz.local_datetime(2018, 2, 1, 7, 30, 0)
# => #<TZInfo::DateTimeWithOffset: 2018-02-01T07:30:00-05:00 ((2458151j,45000s,0n),-18000s,2299161j)>
tz.local_timestamp(2018, 2, 1, 7, 30, 0)
# => #<TZInfo::TimestampWithOffset: @value=1517488200, @sub_second=0, @utc_offset=-18000, @utc=false>

The local_to_utc, local_time, local_datetime and local_timestamp methods may raise a TZInfo::PeriodNotFound or a TZInfo::AmbiguousTime exception. TZInfo::PeriodNotFound signals that there is no equivalent UTC time (for example, during the transition from standard time to daylight savings time when the clocks are moved forward and an hour is skipped). TZInfo::AmbiguousTime signals that there is more than one equivalent UTC time (for example, during the transition from daylight savings time to standard time where the clocks are moved back and an hour is repeated):

tz.local_time(2018, 3, 11, 2, 30, 0, 0)
# raises TZInfo::PeriodNotFound (2018-03-11 02:30:00 is an invalid local time.)
tz.local_time(2018, 11, 4, 1, 30, 0, 0)
# raises TZInfo::AmbiguousTime (2018-11-04 01:30:00 is an ambiguous local time.)

TZInfo::PeriodNotFound exceptions can only be resolved by adjusting the time, for example, by advancing an hour:

tz.local_time(2018, 3, 11, 3, 30, 0, 0)
# => 2018-03-11 03:30:00 -0400

TZInfo::AmbiguousTime exceptions can be resolved by setting the dst parameter and/or specifying a block to choose one of the interpretations:

tz.local_time(2018, 11, 4, 1, 30, 0, 0, true)
# => 2018-11-04 01:30:00 -0400
tz.local_time(2018, 11, 4, 1, 30, 0, 0, false)
# => 2018-11-04 01:30:00 -0500

tz.local_time(2018, 11, 4, 1, 30, 0, 0) {|p| p.first }
# => 2018-11-04 01:30:00 -0400
tz.local_time(2018, 11, 4, 1, 30, 0, 0) {|p| p.last }
# => 2018-11-04 01:30:00 -0500

The default value of the dst parameter can also be set globally:

TZInfo::Timezone.default_dst = true
tz.local_time(2018, 11, 4, 1, 30, 0, 0)
# => 2018-11-04 01:30:00 -0400
TZInfo::Timezone.default_dst = false
tz.local_time(2018, 11, 4, 1, 30, 0, 0)
# => 2018-11-04 01:30:00 -0500

TZInfo also provides information about ISO 3166-1 countries and their associated time zones via the TZInfo::Country class.

A list of valid ISO 3166-1 (alpha-2) country codes can be obtained by calling TZInfo::Country.all_codes:

TZInfo::Country.all_codes
# => ["AD", "AE", ..., "ZW"]

A TZInfo::Country instance representing an individual time zone can be obtained with TZInfo::Country.get:

c = TZInfo::Country.get('US')
# => #<TZInfo::Country: US>
c.name
# => "United States"

The zone_identifiers method returns a list of the time zone identifiers used in a country:

c.zone_identifiers
# => ["America/New_York", "America/Detroit", ..., "Pacific/Honolulu"]

The zone_info method returns further information about the time zones used in a country as an Array of TZInfo::CountryTimezone instances:

zi = c.zone_info.first
zi.identifier               # => "America/New_York"
zi.latitude.to_f.round(5)   # => 40.71417
zi.longitude.to_f.round(5)  # => -74.00639
zi.description              # => "Eastern (most areas)"

The zones method returns an Array of TZInfo::Timezone instances for a country. A TZInfo::Timezone instance can be obtained from a TZInfo::CountryTimezone using the timezone method:

zi.timezone.to_local(Time.utc(2018, 2, 1, 12, 30, 0))
# => 2018-02-01 07:30:00 -0500

For further detail, please refer to the API documentation for the TZInfo::Timezone and TZInfo::Country classes.

Time Zone Selection

The Time Zone Database maintainers recommend that time zone identifiers are not made visible to end-users (see Names of timezones).

Instead of displaying a list of time zone identifiers, time zones can be selected by the user's country. Call TZInfo::Country.all to obtain a list of TZInfo::Country objects, each with a unique code and a name that can be used for display purposes.

Most countries have a single time zone. When choosing such a country, the time zone can be inferred and selected automatically.

croatia = TZInfo::Country.get('HR')
# => #<TZInfo::Country: HR>
croatia.zone_info.length
# => 1
croatia.zone_info[0].identifier
# => "Europe/Belgrade"

Some countries have multiple time zones. The zone_info method can be used to obtain a list of user-friendly descriptions of the available options:

australia = TZInfo::Country.get('AU')
# => #<TZInfo::Country: AU>
australia.zone_info.length
# => 13
australia.zone_info.map {|i| [i.identifier, i.description] }
# => [["Australia/Lord_Howe", "Lord Howe Island"],
#     ["Antarctica/Macquarie", "Macquarie Island"],
#     ...
#     ["Australia/Eucla", "Western Australia (Eucla)"]]

Please note that country information available through TZInfo is intended as an aid to help users select a time zone data appropriate for their practical needs. It is not intended to take or endorse any position on legal or territorial claims.

Compatibility

TZInfo v2.0.0 requires a minimum of Ruby MRI 1.9.3 or JRuby 1.7 (in 1.9 mode or later).

Thread-Safety

The TZInfo::Country and TZInfo::Timezone classes are thread-safe. It is safe to use class and instance methods of TZInfo::Country and TZInfo::Timezone in concurrently executing threads. Instances of both classes can be shared across thread boundaries.

Documentation

API documentation for TZInfo is available on RubyDoc.info.

License

TZInfo is released under the MIT license, see LICENSE for details.

Source Code

Source code for TZInfo is available on GitHub.

Issue Tracker

Please post any bugs, issues, feature requests or questions about TZInfo to the GitHub issue tracker.

Issues with the underlying time zone data should be raised on the Time Zone Database Discussion mailing list.