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].
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.
| 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, or return None, the standard repr() is used.
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 :py:mod:`IPython.lib.pretty`.
More powerful methods
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.