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# 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 `$IPYTHONDIR/extensions/`.

## Getting extensions

A few important extensions are bundled with IPython. Others can be found on the extensions index on the wiki, and installed with the `%install_ext` magic function.

## Using extensions

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

    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 `load_ipython_extension()` function is called after your extension is imported, and the currently active `InteractiveShell` instance is passed as the only argument. You can do anything you want with IPython at that point.

`load_ipython_extension()` will be called again if you load or reload the extension again. It is up to the extension author to add code to manage that.

Useful `InteractiveShell` methods include `register_magic_function()`, `push()` (to add variables to the user namespace) and `drop_by_id()` (to remove variables on unloading).

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 `os.path.join(ip.ipython_dir, 'extensions')`. This directory is added to `sys.path` automatically.

When your extension is ready for general use, please add it to the extensions index.

## Extensions bundled with IPython

- autoreload
- cythonmagic
- octavemagic
- rmagic
- storemagic
- sympyprinting

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