Incompatibility with Dash v2.1.0

[t89]

Quick-Fix on User-Level

If you are a user and looking for a quick fix do this:

$ python -m pip uninstall dash
$ python -m pip install 'dash==2.0.0'

Cause

I spent the past 30 minutes diving through the source code of both projects and I would assume it has to do with:
plotly/dash#1876

Problem

Running the following lines always leads to the AttributeError below:

from jupyter_dash import JupyterDash
app = JupyterDash(__name__)
app.run_server(mode='inline')

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Input In [12], in <module>
      1 from jupyter_dash import JupyterDash
      2 app = JupyterDash()
----> 3 app.run_server(mode='inline')

File ~\.pyenv\pyenv-win\versions\3.10.2\lib\site-packages\jupyter_dash\jupyter_app.py:231, in JupyterDash.run_server(self, mode, width, height, inline_exceptions, **kwargs)
    229 else:
    230     requests_pathname_prefix = '/'
--> 231 self.config.update({'requests_pathname_prefix': requests_pathname_prefix})
    233 # Compute server_url url
    234 if self.server_url is None:

File ~\.pyenv\pyenv-win\versions\3.10.2\lib\site-packages\dash\_utils.py:169, in AttributeDict.update(self, other)
    166 def update(self, other):
    167     # Overrides dict.update() to use __setitem__ above
    168     for k, v in other.items():
--> 169         self[k] = v

File ~\.pyenv\pyenv-win\versions\3.10.2\lib\site-packages\dash\_utils.py:158, in AttributeDict.__setitem__(self, key, val)
    156 def __setitem__(self, key, val):
    157     if key in self.__dict__.get("_read_only", {}):
--> 158         raise AttributeError(self._read_only[key], key)
    160     final_msg = self.__dict__.get("_final")
    161     if final_msg and key not in self:

AttributeError: ('Read-only: can only be set in the Dash constructor or during init_app()', 'requests_pathname_prefix')

[t89]

plotly/dash@bea2697

[jborman-exos]

I wrote the PR linked above - the issue seems to stem from how this package's JupyterDash is subclassing the original Dash app class, specifically this line here.

JupyterDash appears to be trying to modify the config.requests_pathname_prefix after its internal Flask server has been initialized. JupyterDash should either specify this kwarg during __init__() of the parent Dash class or utilize the delayed Flask server init pattern: .init_app(server=flask_server, requests_pathname_prefix=...).

I don't use this package nor am I familiar with its internals, someone familiar with this repo should make the change.

[kennethleungty]

Facing the same problem here, looking forward to this getting resolved!

[rshih32]

+1 on this

[jonasvdd]

+1 on this

[alexcjohnson]

Ha, JupyterDash was exploiting a loophole in the way Dash locked the parts of its config that it deems risky to set late - @t89 you're correct that this is due to plotly/dash#1876 where we closed the .update loophole.

We're working on a fix for this - just need to figure out whether it's better to continue working around the lock here, or if the fact that this is safe for JupyterDash means it's safe for Dash.

In the meantime, add this before your app.run_server call and it'll work with Dash 2.1:

del app.config._read_only["requests_pathname_prefix"]