# 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

The notebook and the Qt console can display richer representations of objects. To use this, you can define any of a number of `_repr_*_()` methods. Note that these are surrounded by single, not double underscores.

Both the notebook and the Qt console can display `svg`, `png` and `jpeg` representations. The notebook can also display `html`, `javascript`, and `latex`. If the methods don’t exist, or return `None`, it falls back to a standard `repr()`.

For example:

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

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

## 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.