Important

This documentation covers IPython versions 6.0 and higher. Beginning with version 6.0, IPython stopped supporting compatibility with Python versions lower than 3.3 including all versions of Python 2.7.

If you are looking for an IPython version compatible with Python 2.7, please use the IPython 5.x LTS release and refer to its documentation (LTS is the long term support release).

# Integrating your objects with IPython

## Tab completion

To change the attributes displayed by tab-completing your object, define a `__dir__(self)` method for it. For more details, see the documentation of the built-in dir() function.

You can also customise key completions for your objects, e.g. pressing tab after `obj["a`. To do so, define a method `_ipython_key_completions_()`, which returns a list of objects which are possible keys in a subscript expression `obj[key]`.

New in version 5.0: Custom key completions

## Rich display

### Custom methods

IPython can display richer representations of objects. To do this, you can define `_ipython_display_()`, or any of a number of `_repr_*_()` methods. Note that these are surrounded by single, not double underscores.

Supported `_repr_*_` methods
Format | REPL | Notebook | Qt Console
--- | --- | --- | ---
`_repr_pretty_` | yes | yes | yes
`_repr_svg_` | no | yes | yes
`_repr_png_` | no | yes | yes
`_repr_jpeg_` | no | yes | yes
`_repr_html_` | no | yes | no
`_repr_javascript_` | no | yes | no
`_repr_markdown_` | no | yes | no
`_repr_latex_` | no | yes | no
`_repr_mimebundle_` | no | ? | ?

If the methods don’t exist, the standard `repr()` is used. If a method exists and returns `None`, it is treated the same as if it does not exist. In general, all available formatters will be called when an object is displayed, and it is up to the UI to select which to display. A given formatter should not generally change its output based on what other formats are available - that should be handled at a different level, such as the `DisplayFormatter`, or configuration.

`_repr_*_` methods should return data of the expected format and have no side effects. For example, `_repr_html_` should return HTML as a `str` and `_repr_png_` should return PNG data as `bytes`.

If you wish to take control of display via your own side effects, use `_ipython_display_()`.

For example:

    class Shout(object):
        def __init__(self, text):
            self.text = text

        def _repr_html_(self):
            return "<h1>" + self.text + "</h1>"

#### Special methods

##### Pretty printing

To customize how your object is pretty-printed, add a `_repr_pretty_` method to the class. The method should accept a pretty printer, and a boolean that indicates whether the printer detected a cycle. The method should act on the printer to produce your customized pretty output. Here is an example:

    class MyObject(object):

        def _repr_pretty_(self, p, cycle):
            if cycle:
                p.text('MyObject(...)')
            else:
                p.text('MyObject[...]')

For details on how to use the pretty printer, see `IPython.lib.pretty`.

##### More powerful methods

class MyObject
  _repr_mimebundle_(include=None, exclude=None)

    Should return a dictionary of multiple formats, keyed by mimetype, or a tuple of two dictionaries: data, metadata (see Metadata). If this returns something, other `_repr_*_` methods are ignored. The method should take keyword arguments `include` and `exclude`, though it is not required to respect them.

  _ipython_display_()

    Displays the object as a side effect; the return value is ignored. If this is defined, all other display methods are ignored.

#### Metadata

We often want to provide frontends with guidance on how to display the data. To support this, `_repr_*_()` methods (except `_repr_pretty_`?) can also return a `(data, metadata)` tuple where `metadata` is a dictionary containing arbitrary key-value pairs for the frontend to interpret. An example use case is `_repr_jpeg_()`, which can be set to return a jpeg image and a `{'height': 400, 'width': 600}` dictionary to inform the frontend how to size the image.

### Formatters for third-party types

The user can also register formatters for types without modifying the class:

    from bar.baz import Foo

    def foo_html(obj):
        return '<marquee>Foo object %s</marquee>' % obj.name

    html_formatter = get_ipython().display_formatter.formatters['text/html']
    html_formatter.for_type(Foo, foo_html)

    # Or register a type without importing it - this does the same as above:
    html_formatter.for_type_by_name('bar.baz', 'Foo', foo_html)

## Custom exception tracebacks

Rarely, you might want to display a custom traceback when reporting an exception. To do this, define the custom traceback using `_render_traceback_(self)` method which returns a list of strings, one string for each line of the traceback. For example, the ipyparallel a parallel computing framework for IPython, does this to display errors from multiple engines.

Please be conservative in using this feature; by replacing the default traceback you may hide important information from the user.