The most complicated plugin included in the JupyterLab application is the Notebook plugin.
Structure of the Notebook plugin¶
The Notebook plugin provides a model and widgets for dealing with notebook files.
The NotebookModel contains an observable list of cells.
A cell model can be:
- a code cell
- a markdown cell
- raw cell
A code cell contains a list of output models. The list of cells and the list of outputs can be observed for changes.
The NotebookModel cell list supports single-step operations such as moving, adding, or deleting cells. Compound cell list operations, such as undo/redo, are also supported by the NotebookModel. Right now, undo/redo is only supported on cells and is not supported on notebook attributes, such as notebook metadata. Currently, undo/redo for individual cell input content is supported by the CodeMirror editor’s undo feature. (Note: CodeMirror editor’s undo does not cover cell metadata changes.)
Cursors and metadata¶
The notebook model and the cell model (i.e. notebook cells) support getting and setting metadata through cursors. You may request a cursor to write to a specific metadata key from a notebook model or a cell model.
After the NotebookModel is created, the NotebookWidgetFactory constructs a new NotebookPanel from the model. The NotebookPanel widget is added to the DockPanel. The NotebookPanel contains:
The NotebookPanel also adds completion logic.
The NotebookToolbar maintains a list of widgets to add to the toolbar. The Notebook widget contains the rendering of the notebook and handles most of the interaction logic with the notebook itself (such as keeping track of interactions such as selected and active cells and also the current edit/command mode).
The NotebookModel cell list provides ways to do fine-grained changes to the cell list.
Higher level actions using NotebookActions¶
Higher-level actions are contained in the NotebookActions namespace, which has functions, when given a notebook widget, to run a cell and select the next cell, merge or split cells at the cursor, delete selected cells, etc.
A Notebook widget contains a list of cell widgets, corresponding to the cell models in its cell list.
- Each cell widget contains an InputAreaWidget,
- which contains n CodeEditorWidget,
- which contains n CodeEditorWidget,
also contains an OutputAreaWidget.
An OutputAreaWidget is responsible for rendering the outputs in the
list. An OutputAreaWidget uses a
object to render
display_data output messages.
Rendering output messages¶
A Rendermime plugin provides a pluggable system for rendering output messages. Default renderers are provided for markdown, html, images, text, etc. Extensions can register renderers to be used across the entire application by registering a handler and mimetype in the rendermime registry. When a notebook is created, it copies the global Rendermime singleton so that notebook-specific renderers can be added. The ipywidgets widget manager is an example of an extension that adds a notebook-specific renderer, since rendering a widget depends on notebook-specific widget state.
How to extend the Notebook plugin¶
We’ll walk through two notebook extensions:
- adding a button to the toolbar
- adding an ipywidgets extension
The ipywidgets third party extension¶
This discussion will be a bit confusing since we’ve been using the term widget to refer to phosphor widgets. In the discussion below, ipython widgets will be referred to as ipywidgets. There is no intrinsic relation between phosphor widgets and ipython widgets.
The ipywidgets extension registers a factory for a notebook widget extension
using the Document Registry.
createNew() function is called with a NotebookPanel and DocumentContext.
The plugin then creates a ipywidget manager (which uses the context to
interact the kernel and kernel’s comm manager). The plugin then registers an
ipywidget renderer with the notebook instance’s rendermime (which is specific
to that particular notebook).
When an ipywidget model is created in the kernel, a comm message is sent to
the browser and handled by the ipywidget manager to create a browser-side
ipywidget model. When the model is displayed in the kernel, a
output is sent to the browser with the ipywidget model id. The renderer
registered in that notebook’s rendermime is asked to render the output. The
renderer asks the ipywidget manager instance to render the corresponding
phosphor widget which it hands back synchronously to the
OutputAreaWidget, and then fills the container with the rendered ipywidget
when the promise resolves.
Note: The ipywidgets third party extension has not yet been released.