panel-mde

A rich text editor for Panel whose value is markdown, powered by EasyMDE.

pn.widgets.TextEditor is Quill-based and gives you HTML, with no way to write a table. MarkdownEditor reads and writes markdown source instead, so the editor, the rendered output and anything else that touches the text all agree on one format.

Features

• Markdown in, markdown out - value is the markdown source, synced on every keystroke
• A toolbar with tables - bold, italic, headings, lists, links, images, tables, undo/redo and more
• Caret-safe programmatic writes - appending to value from Python keeps the caret, selection, scroll position and undo history intact
• Live preview - optional, rendered by Panel's own markdown-it pane so it matches every other markdown surface in your app
• Self-contained - the script, stylesheet and icons ship with the package, so nothing is fetched from a third-party CDN at runtime
• Works in shadow roots and dialogs - inline SVG icons need no @font-face, and the editor re-measures itself when it is attached after render

Installation

Install via pip:

pip install panel-mde

Or via conda:

conda install -c conda-forge panel-mde

Quick Start

import panel as pn
from panel_mde import MarkdownEditor

pn.extension()

editor = MarkdownEditor(
    value="# Sprint notes\n\nMarkdown **in**, markdown **out**.",
    preview=True,
    status_bar=True,
    sizing_mode="stretch_width",
    height=430,
)

editor.servable()

Usage Examples

Two-way value sync

value updates on every keystroke, so a watcher (or a reactive expression) sees the text as it is typed:

import panel as pn
from panel_mde import MarkdownEditor

pn.extension()

editor = MarkdownEditor(value="# Title", height=300)
words = pn.pane.Markdown(editor.param.value.rx.pipe(lambda md: f"{len(md.split())} words"))

pn.Row(editor, words).servable()

Pass on_keyup=False to defer value until the editor loses focus or the user presses Ctrl/Cmd+Enter, the same contract as pn.widgets.TextInput. value_input always tracks the live text.

Appending while the user types

Writing value from Python applies the smallest edit that produces the new text, so an append from an upload flow does not disturb the person editing:

import panel as pn
from panel_mde import MarkdownEditor

pn.extension()

editor = MarkdownEditor(value="# Trip report\n\nWe left early.", height=300)
upload = pn.widgets.FileInput(accept=".png,.jpg")


def add_image(event):
    url = store(event.new)  # your own storage
    editor.value += f"\n\n![{upload.filename}]({url})\n"


upload.param.watch(add_image, "value")

pn.Row(editor, upload).servable()

The caret stays where it was, a selection survives, the view does not scroll and undo still walks back through what the user typed.

Choosing the toolbar

from panel_mde import MarkdownEditor

MarkdownEditor(
    toolbar=["bold", "italic", "heading", "|",
             "unordered-list", "ordered-list", "table", "|",
             "link", "image", "|", "undo", "redo"],
)

toolbar=True renders the set above, toolbar=False hides the toolbar, and "|" inserts a separator. panel_mde.TOOLBAR_ACTIONS lists every available action:

bold, italic, strikethrough, heading, heading-smaller, heading-bigger, heading-1, heading-2, heading-3, code, quote, unordered-list, ordered-list, check-list, clean-block, link, image, table, horizontal-rule, undo, redo, preview.

An unknown action raises ValueError rather than silently disappearing.

Live preview

from panel_mde import MarkdownEditor

MarkdownEditor(value="# Title", preview=True, preview_location="bottom", height=500)

The preview renders through pn.pane.Markdown, so it uses markdown-it with your app's own extensions. EasyMDE's bundled marked.js preview is never used, because it renders subtly differently from every other markdown surface in a Panel app. Add "preview" to the toolbar to let the user toggle it, or restyle it by assigning your own pane to preview_pane.

Inside a dialog

CodeMirror measures a detached element as zero-size, which is why some editors come up blank inside a dialog. MarkdownEditor re-measures on render, layout and resize, so it needs no help from the surrounding app:

import panel as pn
from panel_mde import MarkdownEditor

pn.extension()

editor = MarkdownEditor(value="# Notes", height=300)
card = pn.Card(editor, title="Notes", collapsed=True)

card.servable()

API Reference

MarkdownEditor

Assets

Everything the editor needs is served by the Panel server itself. The EasyMDE bundle is compiled into the package, its stylesheet is vendored, and the toolbar icons are inline SVG. EasyMDE's two runtime downloads are both disabled: the Font Awesome icon font (replaced by the inline SVG) and the spell-check dictionaries (replaced by the browser's own checker). Inline SVG inherits currentColor, so the icons also render correctly inside the shadow root Panel gives every component, with no document-level @font-face registration.

Development

This project is managed by pixi.

Setup

git clone https://github.com/panel-extensions/panel-mde
cd panel-mde

pixi run pre-commit-install
pixi run postinstall
pixi run compile
pixi run test

Compiling the bundle

The ESM in src/panel_mde/models/ imports EasyMDE, which panel compile bundles into src/panel_mde/dist/:

pixi run compile        # one-off build
pixi run compile-dev    # rebuild on change

The vendored EasyMDE stylesheet is generated from the pinned npm version, with its @font-face rules and icon-font references stripped:

pixi run vendor-css

Testing

pixi run test                        # unit tests
pixi run -e test-ui test-ui          # Playwright UI tests

Examples

panel serve examples/apps/notes.py examples/apps/image_upload.py --dev

Documentation

The documentation is built with Zensical:

pixi run -e docs docs-serve    # live-reloading preview
pixi run -e docs docs-build    # build into builtdocs/

Pre-commit

Before committing the first time please install pre-commit:

pip install pre-commit
pre-commit install

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

See LICENSE file for details.