Jupyter configuration to auto-export scripts with markdown->comments, even for non-python languages (Julia)

jupyter_notebook_config.py

import io
import os
from notebook.utils import to_api_path

_script_exporter = None
_html_exporter = None

def script_post_save(model, os_path, contents_manager, **kwargs):
    if model['type'] != 'notebook':
        return

    from nbconvert.exporters.script import ScriptExporter
    from nbconvert.exporters.html import HTMLExporter

    global _script_exporter
    if _script_exporter is None:
        _script_exporter = ScriptExporter(parent=contents_manager)
        _script_exporter.template_file = os.path.dirname(__file__) + '/jupyter_script_export_template.tpl'

    global _html_exporter
    if _html_exporter is None:
        _html_exporter = HTMLExporter(parent=contents_manager)
    log = contents_manager.log

    #export_script(_html_exporter, model, os_path, contents_manager, **kwargs)
    export_script(_script_exporter,   model, os_path, contents_manager, **kwargs)

def export_script(exporter, model, os_path, contents_manager, **kwargs):
    """convert notebooks to Python script after save with nbconvert

    replaces `ipython notebook --script`
    """
    base, ext = os.path.splitext(os_path)
    script, resources = exporter.from_filename(os_path)
    script_fname = base + resources.get('output_extension', '.txt')
    log = contents_manager.log
    log.info("Saving script /%s", to_api_path(script_fname, contents_manager.root_dir))
    with io.open(script_fname, 'w', encoding='utf-8') as f:
        f.write(script)


c.FileContentsManager.post_save_hook = script_post_save

jupyter_script_export_template.tpl

{# Lines inside these brackets are comments #}
{#- Brackets with a `-` mean to skip whitespace before or after the block. -#}

{#-
 # This file defines a Jinja Template for converting .ipynb files into scripts
 # for either delve or julia. We need this because the default script exporter
 # doesn't render Markdown for any languages except Python.
 # Exporting the markdown makes github reviews of .ipynb files easier.
 # This template is invoked by our custom `jupyter_notebook_config.py`. You can
 # read more about the Jinja template specification here:
 #   http://jinja.pocoo.org/docs/2.10/templates/#comments
 # and here:
 #   https://nbconvert.readthedocs.io/en/latest/customizing.html
 # And the filter functions used in this file are defined here:
 #   https://github.com/pallets/jinja/blob/master/jinja2/filters.py
 # and here:
 #   https://github.com/jupyter/nbconvert/blob/master/nbconvert/filters/strings.py
 -#}

{#- ---------
 # Lines up here, before the `extends` section, go at the top of the file, before any other
 # content from the notebook itself.
 #----------- -#}

{%- if 'name' in nb.metadata.get('kernelspec', {}) and
    nb.metadata.kernelspec.name == 'julia' -%}
# This file was generated from a Julia language jupyter notebook.
{% endif -%}

{% extends 'script.tpl'%}

{% block markdowncell %}
  {#- Turn the contents of the markdown cell into a wrapped comment block, and trim empty lines. -#}

  {#-
   # NOTE: We used `kernelspec.name` not `language_info.name`, for reasons specific to
   # our custom jupyter kernel. I think `language_info.name` might be more robust?
   -#}
  {%- if 'name' in nb.metadata.get('kernelspec', {}) and
    nb.metadata.kernelspec.name == 'julia' -%}
    {#- Delve language files are now converted to .jl scripts, so use `#` -#}
    {%- set commentprefix = '# ' -%}
  {#-
   # Add other languages here as if-else block, e.g. C++ would use '// '
   -#}
  {%- else -%}
    {%- set commentprefix = '# ' -%}
  {%- endif -%}

  {%- set commentlen = 92-(commentprefix|length) -%}
  {{- '\n' -}}
  {{- commentprefix ~ '-' * commentlen -}}
  {{- '\n' -}}

  {#- Turn the contents of the markdown cell into a wrapped comment block, and trim empty lines. -#}
  {#- Note: `comment_lines` and `wrap_text` are defined in nbconvert/filters/strings.py -#}
  {{- cell.source | wrap_text(width=commentlen) | comment_lines(prefix=commentprefix) | replace(commentprefix~"\n", commentprefix|trim ~ "\n") -}}

  {{- '\n' -}}
  {{- commentprefix ~ '-' * commentlen -}}
  {{- '\n' -}}

{% endblock markdowncell %}