.. _extensions_overview:

==================
IPython extensions
==================

A level above configuration are IPython extensions, Python modules which modify
the behaviour of the shell. They are referred to by an importable module name,
and can be placed anywhere you'd normally import from, or in
``.ipython/extensions/``.

Getting extensions
==================

A few important extensions are :ref:`bundled with IPython <bundled_extensions>`.
Others can be found on the `extensions index
<https://github.com/ipython/ipython/wiki/Extensions-Index>`_ on the wiki, and
the `Framework :: IPython tag <https://pypi.python.org/pypi?:action=browse&c=586>`_
on PyPI.

Extensions on PyPI can be installed using ``pip``, like any other Python package.

Using extensions
================

To load an extension while IPython is running, use the ``%load_ext`` magic:

.. sourcecode:: ipython

    In [1]: %load_ext myextension

To load it each time IPython starts, list it in your configuration file::

    c.InteractiveShellApp.extensions = [
        'myextension'
    ]

Writing extensions
==================

An IPython extension is an importable Python module that has a couple of special
functions to load and unload it. Here is a template::

    # myextension.py

    def load_ipython_extension(ipython):
        # The `ipython` argument is the currently active `InteractiveShell`
        # instance, which can be used in any way. This allows you to register
        # new magics or aliases, for example.

    def unload_ipython_extension(ipython):
        # If you want your extension to be unloadable, put that logic here.

This :func:`load_ipython_extension` function is called after your extension is
imported, and the currently active :class:`~IPython.core.interactiveshell.InteractiveShell`
instance is passed as the only argument. You can do anything you want with
IPython at that point.

:func:`load_ipython_extension` will not be called again if the user use
`%load_extension`.  The user have to explicitly ask the extension to be
reloaded (with `%reload_extension`). In case where the use ask the extension to
be reloaded, , the extension will be unloaded (with
`unload_ipython_extension`), and loaded again. 

Useful :class:`InteractiveShell` methods include :meth:`~IPython.core.interactiveshell.InteractiveShell.register_magic_function`, 
:meth:`~IPython.core.interactiveshell.InteractiveShell.push` (to add variables to the user namespace) and 
:meth:`~IPython.core.interactiveshell.InteractiveShell.drop_by_id` (to remove variables on unloading).

.. seealso::

   :ref:`defining_magics`

You can put your extension modules anywhere you want, as long as they can be
imported by Python's standard import mechanism. However, to make it easy to
write extensions, you can also put your extensions in :file:`extensions/`
within the :ref:`IPython directory <ipythondir>`. This directory is
added to :data:`sys.path` automatically.

When your extension is ready for general use, please add it to the `extensions
index <https://github.com/ipython/ipython/wiki/Extensions-Index>`_. We also
encourage you to upload it to PyPI and use the ``Framework :: IPython``
classifier, so that users can install it with standard packaging tools.

.. _bundled_extensions:

Extensions bundled with IPython
===============================

.. toctree::
   :maxdepth: 1

   autoreload
   storemagic

* ``octavemagic`` used to be bundled, but is now part of `oct2py <http://blink1073.github.io/oct2py/docs/>`_.
  Use ``%load_ext oct2py.ipython`` to load it.
* ``rmagic`` is now part of `rpy2 <http://rpy.sourceforge.net/>`_. Use
  ``%load_ext rpy2.ipython`` to load it, and see :mod:`rpy2.ipython.rmagic` for
  details of how to use it.
* ``cythonmagic`` used to be bundled, but is now part of `cython <https://github.com/cython/cython/>`_
  Use ``%load_ext Cython`` to load it.
* ``sympyprinting`` used to be a bundled extension, but you should now use
  :func:`sympy.init_printing` instead.
