Cannot instantiate JupyterDash instance with fresh install

[rickymagner]

As of Flask 2.3.0, the app.before_first_request decorator has been removed. Since creating a JupyterDash instance depends on this, this means the project as written technically has a flask<2.3.0 dependency. On a fresh install, this defaults to grabbing a Flask version past 2.3.0 and hence cannot be run.

Steps to reproduce

In a new virtual environment, install jupyter-dash. Then in a notebook hooked up to the venv, run:

from jupyter_dash import JupyterDash

app = JupyterDash()

which results in the following error:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[2], line 1
----> 1 app = JupyterDash()

File ~/qb_test/venv/lib/python3.10/site-packages/jupyter_dash/jupyter_app.py:103, in JupyterDash.__init__(self, name, server_url, **kwargs)
     96             warnings.warn(
     97                 "The {prop} argument is ignored when running in Colab".format(
     98                     prop=prop
     99                 )
    100             )
    102 # Call superclass constructor
--> 103 super(JupyterDash, self).__init__(name=name, **kwargs)
    105 if not JupyterDash._in_ipython:
    106     # Nothing else to do when not running in a Jupyter context
    107     return

File ~/qb_test/venv/lib/python3.10/site-packages/dash/dash.py:501, in Dash.__init__(self, name, server, assets_folder, pages_folder, use_pages, assets_url_path, assets_ignore, assets_external_path, eager_loading, include_assets_files, url_base_pathname, requests_pathname_prefix, routes_pathname_prefix, serve_locally, compress, meta_tags, index_string, external_scripts, external_stylesheets, suppress_callback_exceptions, prevent_initial_callbacks, show_undo_redo, extra_hot_reload_paths, plugins, title, update_title, long_callback_manager, background_callback_manager, **obsolete)
    498         plugin.plug(self)
    500 if self.server is not None:
--> 501     self.init_app()
    503 self.logger.setLevel(logging.INFO)

File ~/qb_test/venv/lib/python3.10/site-packages/dash/dash.py:545, in Dash.init_app(self, app, **kwargs)
    542     """Handle a halted callback and return an empty 204 response."""
    543     return "", 204
--> 545 self.server.before_first_request(self._setup_server)
    547 # add a handler for components suites errors to return 404
    548 self.server.errorhandler(InvalidResourceError)(self._invalid_resources_handler)

AttributeError: 'Flask' object has no attribute 'before_first_request'

I don't know enough about the code to suggest a fix, or whether this project is still being maintained at all based on #110, but given the library cannot be used out of the box it seems like at least a small patch should be released.

Workaround

In case anyone stumbles upon this same issue and the project isn't updated any time soon, a quick workaround is to install a lower version of Flask, e.g.

pip install jupyter-dash
pip install Flask==2.2.0

This is less than ideal, since you won't be able to upgrade Flask ever, but will at least let you create a JupyterDash instance. I haven't tested if this might break anything else in the package.

[alexcjohnson]

FYI two things:

1. We're about to place an upper limit on the Flask version installed with dash because of repeated issues like this Upper bound on Flask and Werkzeug versions dash#2538
2. This entire package is about to be obsolete, when we merge its functionality into the main dash package Merge JupyterDash with Dash dash#2530

[alexcjohnson]

That said, I think you have an old version of Dash installed (check dash.__version__) - in plotly/dash#2265 (part of Dash v2.7.0) we removed that before_first request call.

[rickymagner]

Those are all great to hear, especially that this project will get merged into the main Dash package. You're right, I had a slightly older version of Dash as well, so upgrading that should do the trick too. Thanks!