DESCRIPTION

pytz - World Timezone Definitions for Python
============================================

:Author: Stuart Bishop <stuart@stuartbishop.net>

Introduction
~~~~~~~~~~~~

pytz brings the Olson tz database into Python. This library allows
accurate and cross platform timezone calculations using Python 2.4
or higher. It also solves the issue of ambiguous times at the end
of daylight saving time, which you can read more about in the Python
Library Reference (``datetime.tzinfo``).

Almost all of the Olson timezones are supported.

.. note::

    This library differs from the documented Python API for
    tzinfo implementations; if you want to create local wallclock
    times you need to use the ``localize()`` method documented in this
    document. In addition, if you perform date arithmetic on local
    times that cross DST boundaries, the result may be in an incorrect
    timezone (ie. subtract 1 minute from 2002-10-27 1:00 EST and you get
    2002-10-27 0:59 EST instead of the correct 2002-10-27 1:59 EDT). A
    ``normalize()`` method is provided to correct this. Unfortunately these
    issues cannot be resolved without modifying the Python datetime
    implementation (see PEP-431).


Installation
~~~~~~~~~~~~

This package can either be installed using ``pip`` or from a tarball using the
standard Python distutils.

If you are installing using ``pip``, you don't need to download anything as the
latest version will be downloaded for you from PyPI::

    pip install pytz

If you are installing from a tarball, run the following command as an
administrative user::

    python setup.py install


pytz for Enterprise
~~~~~~~~~~~~~~~~~~~

Available as part of the Tidelift Subscription.

The maintainers of pytz and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. `Learn more. <https://tidelift.com/subscription/pkg/pypi-pytz?utm_source=pypi-pytz&utm_medium=referral&utm_campaign=enterprise&utm_term=repo>`_.


Example & Usage
~~~~~~~~~~~~~~~

Localized times and date arithmetic
-----------------------------------

>>> from datetime import datetime, timedelta
>>> from pytz import timezone
>>> import pytz
>>> utc = pytz.utc
>>> utc.zone
'UTC'
>>> eastern = timezone('US/Eastern')
>>> eastern.zone
'US/Eastern'
>>> amsterdam = timezone('Europe/Amsterdam')
>>> fmt = '%Y-%m-%d %H:%M:%S %Z%z'

This library only supports two ways of building a localized time. The
first is to use the ``localize()`` method provided by the pytz library.
This is used to localize a naive datetime (datetime with no timezone
information):

>>> loc_dt = eastern.localize(datetime(2002, 10, 27, 6, 0, 0))
>>> print(loc_dt.strftime(fmt))
2002-10-27 06:00:00 EST-0500

The second way of building a localized time is by converting an existing
localized time using the standard ``astimezone()`` method:

>>> ams_dt = loc_dt.astimezone(amsterdam)
>>> ams_dt.strftime(fmt)
'2002-10-27 12:00:00 CET+0100'

Unfortunately using the tzinfo argument of the standard datetime
constructors ''does not work'' with pytz for many timezones.

>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=amsterdam).strftime(fmt)  # /!\ Does not work this way!
'2002-10-27 12:00:00 LMT+0020'

It is safe for timezones without daylight saving transitions though, such
as UTC:

>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=pytz.utc).strftime(fmt)  # /!\ Not recommended except for UTC
'2002-10-27 12:00:00 UTC+0000'

The preferred way of dealing with times is to always work in UTC,
converting to localtime only when generating output to be read
by humans.

>>> utc_dt = datetime(2002, 10, 27, 6, 0, 0, tzinfo=utc)
>>> loc_dt = utc_dt.astimezone(eastern)
>>> loc_dt.strftime(fmt)
'2002-10-27 01:00:00 EST-0500'

This library also allows you to do date arithmetic using local
times, although it is more complicated than working in UTC as you
need to use the ``normalize()`` method to handle daylight saving time
and other timezone transitions. In this example, ``loc_dt`` is set
to the instant when daylight saving time ends in the US/Eastern
timezone.

>>> before = loc_dt - timedelta(minutes=10)
>>> before.strftime(fmt)
'2002-10-27 00:50:00 EST-0500'
>>> eastern.normalize(before).strftime(fmt)
'2002-10-27 01:50:00 EDT-0400'
>>> after = eastern.normalize(before + timedelta(minutes=20))
>>> after.strftime(fmt)
'2002-10-27 01:10:00 EST-0500'

Creating local times is also tricky, and the reason why working with
local times is not recommended. Unfortunately, you cannot just pass
a ``tzinfo`` argument when constructing a datetime (see the next
section for more details)

>>> dt = datetime(2002, 10, 27, 1, 30, 0)
>>> dt1 = eastern.localize(dt, is_dst=True)
>>> dt1.strftime(fmt)
'2002-10-27 01:30:00 EDT-0400'
>>> dt2 = eastern.localize(dt, is_dst=False)
>>> dt2.strftime(fmt)
'2002-10-27 01:30:00 EST-0500'

Converting between timezones is more easily done, using the
standard astimezone method.

>>> utc_dt = utc.localize(datetime.utcfromtimestamp[PII_REDACTED]))
>>> utc_dt.strftime(fmt)
'2006-03-26 21:34:59 UTC+0000'
>>> au_tz = timezone('Australia/Sydney')
>>> au_dt = utc_dt.astimezone(au_tz)
>>> au_dt.strftime(fmt)
'2006-03-27 08:34:59 AEDT+1100'
>>> utc_dt2 = au_dt.astimezone(utc)
>>> utc_dt2.strftime(fmt)
'2006-03-26 21:34:59 UTC+0000'
>>> utc_dt == utc_dt2
True

You can take shortcuts when dealing with the UTC side of timezone
conversions. ``normalize()`` and ``localize()`` are not really
necessary when there are no daylight saving time transitions to
deal with.

>>> utc_dt = datetime.utcfromtimestamp[PII_REDACTED]).replace(tzinfo=utc)
>>> utc_dt.strftime(fmt)
'2006-03-26 21:34:59 UTC+0000'
>>> au_tz = timezone('Australia/Sydney')
>>> au_dt = au_tz.normalize(utc_dt.astimezone(au_tz))
>>> au_dt.strftime(fmt)
'2006-03-27 08:34:59 AEDT+1100'
>>> utc_dt2 = au_dt.astimezone(utc)
>>> utc_dt2.strftime(fmt)
'2006-03-26 21:34:59 UTC+0000'


``tzinfo`` API
--------------

The ``tzinfo`` instances returned by the ``timezone()`` function have
been extended to cope with ambiguous times by adding an ``is_dst``
parameter to the ``utcoffset()``, ``dst()`` && ``tzname()`` methods.

>>> tz = timezone('America/St_Johns')

>>> normal = datetime(2009, 9, 1)
>>> ambiguous = datetime(2009, 10, 31, 23, 30)

The ``is_dst`` parameter is ignored for most timestamps. It is only used
during DST transition ambiguous periods to resolve that ambiguity.

>>> print(tz.utcoffset(normal, is_dst=True))
-1 day, 21:30:00
>>> print(tz.dst(normal, is_dst=True))
1:00:00
>>> tz.tzname(normal, is_dst=True)
'NDT'

>>> print(tz.utcoffset(ambiguous, is_dst=True))
-1 day, 21:30:00
>>> print(tz.dst(ambiguous, is_dst=True))
1:00:00
>>> tz.tzname(ambiguous, is_dst=True)
'NDT'

>>> print(tz.utcoffset(normal, is_dst=False))
-1 day, 21:30:00
>>> tz.dst(normal, is_dst=False)
datetime.timedelta(0, 3600)
>>> tz.tzname(normal