A 2to3 converter

This nbextension converts python2 code in notebook code cells to python3 code.

Under the hood, it uses a call to the current notebook kernel to reformat the code. The conversion run by the kernel uses Python’s standard-library lib2to3 module.

The nbextension provides

• a toolbar button (configurable to be added or not)
• a keyboard shortcut for reformatting the current code-cell (default shortcut is Ctrl-M, can also be configured not to add the keyboard shortcut).
• a keyboard shortcut for reformatting the whole notebook (default shortcut is Ctrl-Shift-M, can also be configured not to add the keyboard shortcut).

Syntax needs to be correct, but the nbextension may be able to point out basic syntax errors.

Options

All options are provided by the KerneExecOnCells library - see the internals section below for details. There are a few nbextension-wide options, configurable using the jupyter_nbextensions_configurator or by editing the notebook section config file directly. The options are as follows:

• 2to3.add_toolbar_button: Whether to add a toolbar button to transform the selected cell(s). Defaults to true.

• 2to3.button_icon: A font-awesome class defining the icon used for the toolbar button and actions. See fontawesome for available icon classes. Defaults to fa-legal.

• 2to3.button_label: Toolbar button label text. Also used in the actions’ help text. Defaults to Convert Python 2 to 3.

• 2to3.register_hotkey: Whether to register hotkeys to transform the selected cell(s)/whole notebook. Defaults to true.

• 2to3.hotkeys.process_all: Hotkey to use to transform all the code cells in the notebook. Defaults to Ctrl-Shift-L.

• 2to3.hotkeys.process_selected: Hotkey to use to transform the selected cell(s). Defaults to Ctrl-L.

• 2to3.show_alerts_for_errors: Whether to show alerts for errors in the kernel calls. Defaults to true.

• 2to3.kernel_config_map_json: The value of this key is a string which can be parsed into a json object giving the config for each kernel language.

  The following give the per-kernel options of the parsed json, using the language key python:

  • 2to3.kernel_config_map_json.python.library: String to execute in the kernel in order to load any necessary kernel libraries.
  • 2to3.kernel_config_map_json.python.replacements_json_to_kernel: a list of pairs of strings, used as arguments to javascript’s String.replace(from, to) to translate from a json string into a valid representation of the same string in the kernel language. Since json strings are particularly simple, this can often (as with the python language) be left as the default, an empty list.
  • 2to3.kernel_config_map_json.python.prefix and 2to3.kernel_config_map_json.python.postfix: Strings added as bookends to the kernel string (translated from the json string using the replacements above) to make up the kernel prettifier call kernel’s prettifier libraries.
  • 2to3.kernel_config_map_json.python.trim_formatted_text: Whether to trim whitespace from the transformed cell text. Since jupyter cells don’t usually have leading or trailing whitespace, the default behaviour is to trim the transformed text, in order to prevent the transform adding extra newlines at the end (a common behaviour for source files, where having a trailing newline is often considered good practice).

Internals

Under the hood, this nbextension uses the KerneExecOnCells library, a shared library for creating Jupyter nbextensions which transform code cell text using calls to the active kernel.

See the shared README for the internal model used by the nbextension.

History

The project was forked by @EWouters from @jfbercher‘s code_prettify, retaining most of the code.

It has since been altered to use the KerneExecOnCells library, a shared library for creating Jupyter nbextensions which transform code cell text using calls to the active kernel.

The 2to3 conversion’s kernel-side python code is based on 2to3_nb.py by @takluyver and @fperez.

It could be extended to use the futurize functions so it can convert both ways.