Custom request handlers

The notebook webserver can be interacted with using a well defined RESTful API. You can define custom RESTful API handlers in addition to the ones provided by the notebook. As described below, to define a custom handler you need to first write a notebook server extension. Then, in the extension, you can register the custom handler.

Writing a notebook server extension

The notebook webserver is written in Python, hence your server extension should be written in Python too. Server extensions, like IPython extensions, are Python modules that define a specially named load function, load_jupyter_server_extension. This function is called when the extension is loaded.

def load_jupyter_server_extension(nb_server_app):
    """
    Called when the extension is loaded.

    Args:
        nb_server_app (NotebookWebApplication): handle to the Notebook webserver instance.
    """
    pass

To get the notebook server to load your custom extension, you’ll need to add it to the list of extensions to be loaded. You can do this using the config system. NotebookApp.server_extensions is a config variable which is an array of strings, each a Python module to be imported. Because this variable is notebook config, you can set it two different ways, using config files or via the command line.

For example, to get your extension to load via the command line add a double dash before the variable name, and put the Python array in double quotes. If your package is “mypackage” and module is “mymodule”, this would look like jupyter notebook --NotebookApp.server_extensions="['mypackage.mymodule']" . Basically the string should be Python importable.

Alternatively, you can have your extension loaded regardless of the command line args by setting the variable in the Jupyter config file. The default location of the Jupyter config file is ~/.jupyter/profile_default/jupyter_notebook_config.py. Then, inside the config file, you can use Python to set the variable. For example, the following config does the same as the previous command line example [1].

c = get_config()
c.NotebookApp.server_extensions = [
    'mypackage.mymodule'
]

Before continuing, it’s a good idea to verify that your extension is being loaded. Use a print statement to print something unique. Launch the notebook server and you should see your statement printed to the console.

Registering custom handlers

Once you’ve defined a server extension, you can register custom handlers because you have a handle to the Notebook server app instance (nb_server_app above). However, you first need to define your custom handler. To declare a custom handler, inherit from notebook.base.handlers.IPythonHandler. The example below[1] is a Hello World handler:

from notebook.base.handlers import IPythonHandler

class HelloWorldHandler(IPythonHandler):
    def get(self):
        self.finish('Hello, world!')

The Jupyter Notebook server use Tornado as its web framework. For more information on how to implement request handlers, refer to the Tornado documentation on the matter.

After defining the handler, you need to register the handler with the Notebook server. See the following example:

web_app = nb_server_app.web_app
host_pattern = '.*$'
route_pattern = url_path_join(web_app.settings['base_url'], '/hello')
web_app.add_handlers(host_pattern, [(route_pattern, HelloWorldHandler)])

Putting this together with the extension code, the example looks like the following:

from notebook.utils import url_path_join
from notebook.base.handlers import IPythonHandler

class HelloWorldHandler(IPythonHandler):
    def get(self):
        self.finish('Hello, world!')

def load_jupyter_server_extension(nb_server_app):
    """
    Called when the extension is loaded.

    Args:
        nb_server_app (NotebookWebApplication): handle to the Notebook webserver instance.
    """
    web_app = nb_server_app.web_app
    host_pattern = '.*$'
    route_pattern = url_path_join(web_app.settings['base_url'], '/hello')
    web_app.add_handlers(host_pattern, [(route_pattern, HelloWorldHandler)])

References:

  1. Peter Parente’s Mindtrove