Pendulum
########

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Python datetimes made easy.

Supports Python **2.7** and **3.4+**.


.. code-block:: python

   >>> import pendulum

   >>> now_in_paris = pendulum.now('Europe/Paris')
   >>> now_in_paris
   '2016-07-04T00:49:58.502116+02:00'

   # Seamless timezone switching
   >>> now_in_paris.in_timezone('UTC')
   '2016-07-03T22:49:58.502116+00:00'

   >>> tomorrow = pendulum.now().add(days=1)
   >>> last_week = pendulum.now().subtract(weeks=1)

   >>> past = pendulum.now().subtract(minutes=2)
   >>> past.diff_for_humans()
   >>> '2 minutes ago'

   >>> delta = past - last_week
   >>> delta.hours
   23
   >>> delta.in_words(locale='en')
   '6 days 23 hours 58 minutes'

   # Proper handling of datetime normalization
   >>> pendulum.datetime(2013, 3, 31, 2, 30, tz='Europe/Paris')
   '2013-03-31T03:30:00+02:00' # 2:30 does not exist (Skipped time)

   # Proper handling of dst transitions
   >>> just_before = pendulum.datetime(2013, 3, 31, 1, 59, 59, 999999, tz='Europe/Paris')
   '2013-03-31T01:59:59.999999+01:00'
   >>> just_before.add(microseconds=1)
   '2013-03-31T03:00:00+02:00'


Why Pendulum?
=============

Native ``datetime`` instances are enough for basic cases but when you face more complex use-cases
they often show limitations and are not so intuitive to work with.
``Pendulum`` provides a cleaner and more easy to use API while still relying on the standard library.
So it's still ``datetime`` but better.

Unlike other datetime libraries for Python, Pendulum is a drop-in replacement
for the standard ``datetime`` class (it inherits from it), so, basically, you can replace all your ``datetime``
instances by ``DateTime`` instances in you code (exceptions exist for libraries that check
the type of the objects by using the ``type`` function like ``sqlite3`` or ``PyMySQL`` for instance).

It also removes the notion of naive datetimes: each ``Pendulum`` instance is timezone-aware
and by default in ``UTC`` for ease of use.

Pendulum also improves the standard ``timedelta`` class by providing more intuitive methods and properties.


Why not Arrow?
==============

Arrow is the most popular datetime library for Python right now, however its behavior
and API can be erratic and unpredictable. The ``get()`` method can receive pretty much anything
and it will try its best to return something while silently failing to handle some cases:

.. code-block:: python

    arrow.get('2016-1-17')
    # <Arrow [2016-01-01T00:00:00+00:00]>

    pendulum.parse('2016-1-17')
    # <Pendulum [2016-01-17T00:00:00+00:00]>

    arrow.get('20160413')
    # <Arrow [1970-08-22T08:06:53+00:00]>

    pendulum.parse('20160413')
    # <Pendulum [2016-04-13T00:00:00+00:00]>

    arrow.get('2016-W07-5')
    # <Arrow [2016-01-01T00:00:00+00:00]>

    pendulum.parse('2016-W07-5')
    # <Pendulum [2016-02-19T00:00:00+00:00]>

    # Working with DST
    just_before = arrow.Arrow(2013, 3, 31, 1, 59, 59, 999999, 'Europe/Paris')
    just_after = just_before.replace(microseconds=1)
    '2013-03-31T02:00:00+02:00'
    # Should be 2013-03-31T03:00:00+02:00

    (just_after.to('utc') - just_before.to('utc')).total_seconds()
    -3599.999999
    # Should be 1e-06

    just_before = pendulum.datetime(2013, 3, 31, 1, 59, 59, 999999, 'Europe/Paris')
    just_after = just_before.add(microseconds=1)
    '2013-03-31T03:00:00+02:00'

    (just_after.in_timezone('utc') - just_before.in_timezone('utc')).total_seconds()
    1e-06

Those are a few examples showing that Arrow cannot always be trusted to have a consistent
behavior with the data you are passing to it.


Limitations
===========

Even though the ``DateTime`` class is a subclass of ``datetime`` there are some rare cases where
it can't replace the native class directly. Here is a list (non-exhaustive) of the reported cases with
a possible solution, if any:

* ``sqlite3`` will use the ``type()`` function to determine the type of the object by default. To work around it you can register a new adapter:

.. code-block:: python

    from pendulum import DateTime
    from sqlite3 import register_adapter

    register_adapter(DateTime, lambda val: val.isoformat(' '))

* ``mysqlclient`` (former ``MySQLdb``) and ``PyMySQL`` will use the ``type()`` function to determine the type of the object by default. To work around it you can register a new adapter:

.. code-block:: python

    import MySQLdb.converters
    import pymysql.converters

    from pendulum import DateTime

    MySQLdb.converters.conversions[DateTime] = MySQLdb.converters.DateTime2literal
    pymysql.converters.conversions[DateTime] = pymysql.converters.escape_datetime

* ``django`` will use the ``isoformat()`` method to store datetimes in the database. However since ``pendulum`` is always timezone aware the offset information will always be returned by ``isoformat()`` raising an error, at least for MySQL databases. To work around it you can either create your own ``DateTimeField`` or use the previous workaround for ``MySQLdb``:

.. code-block:: python

    from django.db.models import DateTimeField as BaseDateTimeField
    from pendulum import DateTime


    class DateTimeField(BaseDateTimeField):

        def value_to_string(self, obj):
            val = self.value_from_object(obj)

            if isinstance(value, DateTime):
                return value.to_datetime_string()

            return '' if val is None else val.isoformat()


Resources
=========

* `Official Website <https://pendulum.eustace.io>`_
* `Documentation <https://pendulum.eustace.io/docs/>`_
* `Issue Tracker <https://github.com/sdispater/pendulum/issues>`_


Contributing
============

Contributions are welcome, especially with localization.

Getting started
---------------

To work on the Pendulum codebase, you'll want to clone the project locally
and install the required depedendencies via `poetry <https://poetry.eustace.io>`_.

.. code-block:: bash

    $ git clone git@github.com:sdispater/pendulum.git
    $ poetry install

Localization
------------

If you want to help with localization, there are two different cases: the locale already exists
or not.

If the locale does not exist you will need to create it by using the ``clock`` utility:

.. code-block:: bash

    ./clock locale create <your-locale>

It will generate a directory in ``pendulum/locales`` named after your locale, with the following
structure:

.. code-block:: text

    <your-locale>/
        - custom.py
        - locale.py

The ``locale.py`` file must not be modified. It contains the translations provided by
the CLDR database.

The ``custom.py`` file is the one you want to modify. It contains the data needed
by Pendulum that are not provided by the CLDR database. You can take the `en <https://github.com/sdispater/pendulum/tree/master/pendulum/locales/en/custom.py>`_
data as a reference to see which data is needed.

You should also add tests for the created or modified locale.
