Callysto

Callysto is a Python framework to create domain-specific kernels for the Jupyter notebook platform. All you have to do is to extend a class BaseKernel and overload its method do_execute_(). This methods receives whatever the user types in the notebook, and is expected to return one or more content frames (using the yield statement), which are rendered then sent to the notebook. That's it! No need to deal with exceptions or MIME type; Callysto does it for you. Callysto also simplifies the process of installing kernels or launching them.

Callysto comes with built-in renderers for basic MIME types (text, PNG, GIF, JPG, SVG, HTML and Javascript documents). Additional renderers can be developed by extending the BaseRenderer class. For example, a Graphviz-based graph renderer is provided to display networks.

Example kernels developed with Callysto are provided as a separate repository.

Quick examples

An 'echo' kernel, returning the user input:

import callysto

class MyKernel (callysto.BaseKernel):
	def do_execute_ (self, code):
		# very simple kernel echoing the user's input
		yield code

if (__name__ == "__main__"):
    MyKernel.launch()

A dummy kernel echoing the user input and also producing a CSV table (rendered as an HTML table):

class MyKernel (callysto.BaseKernel):
	def do_execute_ (self, code):
		# first echo the input code, but in uppercase
		yield code.upper()
		# then return a CSV table
		table = (("column_1", "column_2"),
			     ("value_1", "value_2"))
		yield (callysto.MIME_TYPE.CSV_WITH_HEADER, table)

Magic commands

Callysto provides non-nonsense, IPython-inspired magic commands that can run either on the user code before it is sent to your do_execute_() method (pre-flight commands), or run on the results generated by your method after it runs (post-flight commands). These magic commands can accept options as defined by a simple documentation, and handled by the excellent docopt library:

class MyKernel (callysto.BaseKernel):
	# method called when the kernel is initialized
	def do_startup_ (self, **kwargs):
		# change the prefix of the magic commands from its default '%'
		self.magic_commands.prefix = '!'

		# simple magic command, without options
		self.declare_pre_flight_command(
			"uppercase", lambda x: x.upper())

		# more complex magic command, with options
		def add_prefix (code, **kwargs):
			""" Add a prefix to the input code

				Usage:
					add_prefix [--prefix STRING]

				Options:
					--prefix STRING  Add a prefix [default: >]
			"""
			prefix = kwargs["--prefix"]  # optional; '>' by default
			return prefix + code

		self.declare_pre_flight_command(
			"add-prefix", add_prefix)
	...

Now whenever the user inputs something like this:

!uppercase
!add-prefix --prefix {
test

Then your do_execute_() method will receive the string {TEST. This is because the uppercase magic command will be called first, transforming the user's code to uppercase. Then add-prefix will be called, adding the prefix { to this code. Very useful to pre-process user's input.

Roadmap

• Implementation of code completion mechanisms
• Development of a Vega content renderer

Current version: 0.2 (February 25, 2016)