Dtale not working with Flask 2.2.1

[UFO-101]

Exception on /dtale/main/1 [GET]
Traceback (most recent call last):
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/app.py", line 2525, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/app.py", line 1822, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/app.py", line 1820, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/app.py", line 1796, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/views.py", line 1173, in view_main
    return _view_main(data_id)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/views.py", line 1158, in _view_main
    return base_render_template("dtale/main.html", data_id, title=title, iframe=iframe)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/views.py", line 1127, in base_render_template
    return render_template(
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/templating.py", line 147, in render_template
    return _render(app, template, context)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/templating.py", line 130, in _render
    rv = template.render(context)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/jinja2/environment.py", line 1301, in render
    self.environment.handle_exception()
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/jinja2/environment.py", line 936, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/templates/dtale/main.html", line 1, in top-level template code
    {% extends "dtale/base.html" %}
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/templates/dtale/base.html", line 13, in top-level template code
    <link rel="shortcut icon" href="{{ url_for('static', filename='images/favicon.png') }}">
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/app.py", line 154, in url_for
    return url_for(endpoint, *args, **kwargs)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/helpers.py", line 256, in url_for
    return current_app.url_for(
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/app.py", line 154, in url_for
    return url_for(endpoint, *args, **kwargs)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/helpers.py", line 256, in url_for
    return current_app.url_for(
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/app.py", line 154, in url_for
    return url_for(endpoint, *args, **kwargs)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/helpers.py", line 256, in url_for
    return current_app.url_for(
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/dtale/app.py", line 154, in url_for
    return url_for(endpoint, *args, **kwargs)
  File "/Users/user/.local/share/virtualenvs/streamlit-app-26mcmUwo/lib/python3.10/site-packages/flask/helpers.py", line 256, in url_for
    return current_app.url_for(
...
...
...
  File "/.venv/lib/python3.10/site-packages/flask/helpers.py", line 256, in url_for
    return current_app.url_for(
  File "/.venv/lib/python3.10/site-packages/werkzeug/local.py", line 316, in __get__
    obj = instance._get_current_object()  # type: ignore[misc]
  File "/.venv/lib/python3.10/site-packages/werkzeug/local.py", line 507, in _get_current_object
    obj = local.get()  # type: ignore[union-attr]
  RecursionError: maximum recursion depth exceeded while calling a Python object

Dtale is unable to serve any static assets. The browser shows an Internal Server Error 500.

I reproduced this in several environments (Linux, Mac, running in a notebook, as a script inside Streamlit) with the following script.

import dtale
import pandas as pd

if __name__ == '__main__':
    print('Hello World')
    d = dtale.show(pd.DataFrame([1,2,3,4,5]), subprocess=False)
    print('main_url', d._main_url)

The problem appears to be with either the function url_for in dtale/app.py or the function url_for in flask/helpers.py. If you set the app_root parameter the error goes away and the browser shows just a blank screen.

Fixed by downgrading to Flask 2.1.3.

[carb0nc0py]

I just ran into the same issue. Flask 2.2.1, same error

[tianfy1258]

same, but we can solve the problem by "pip install flask==2.1.3"

[aschonfeld]

Apologies everyone, I've dug in and found that by updating line 155 of dtale/app.py to the following:

return Flask.url_for(self, endpoint, *args, **kwargs)

seems to solve the problem. I'll release a new version soon and let you know when its out there

[aschonfeld]

@carb0nc0py @tianfy1258 @UFO-101 just released v2.7.1 to pypi (conda-forge available shortly) which fixes this issue. Thanks for spotting this & let me know if you have any other issues. Also, if you have done so already, please toss your ⭐ on the repo. Thanks! 🙏