I have an existing dash app that uses dash extensions. I also have installed dask (distributed) to make use of the futures. In order to get this set up I need to create a client like so which is in my results.py:
from dask.distributed import Client as DaskClient
dask_client = DaskClient()
My dash app is structure is like so:
dash/
application.py
index.py
results.py
pathfinder.py
requirements.txt
In order for the futures to work (using the client) I needed to move my imports of results inside my if main block like so:
index.py:
if __name__ == "__main__":
from application import app, server # noqa: F401
from dash import html
from results import results
inner_layout = html.Div(
[
results
],
style={"padding": 20},
)
app.layout = html.Div(children=[inner_layout])
app.run_server(debug=False)
Within my application.py the setup is like so:
from dash_extensions.enrich import DashProxy, MultiplexerTransform, ServersideOutputTransform
import dash_bootstrap_components as dbc
# external CSS stylesheets
external_stylesheets = [
dbc.themes.LUX, # dash-bootstrap theme
"https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.2/css/all.min.css", # font-awesome icons
]
meta_tags = [{"name": "viewport", "content": "width=device-width, initial-scale=1.0"}]
app = DashProxy(
__name__,
external_stylesheets=external_stylesheets,
meta_tags=meta_tags,
url_base_pathname="/analyzer/",
title="Proj",
suppress_callback_exceptions=True,
transforms=[MultiplexerTransform(), ServersideOutputTransform()]
)
server = app.server
results.py
import dash_bootstrap_components as dbc
from dash import dcc
from dash import html
from dash.dependencies import Input, Output, State
from application import app
from dash.exceptions import PreventUpdate
from pathfinder import find_all_paths
from dash_extensions.enrich import ServersideOutput
from dask.distributed import Client as DaskClient
dask_client = DaskClient()
futures = {}
results = html.Div(
[
dbc.Row(
[
html.Button(id="analysis-button", children='Take a nap'),
html.Div(id="results"),
dcc.Store(id="result-tuple"),
dcc.Interval(id="poller", max_intervals=0)
],
class_name="text-center",
),
]
)
@app.callback(
Output("analysis-button", "disabled"),
Output("analysis-button", "children"),
ServersideOutput("result-tuple", "data"),
Output("poller", "max_intervals"),
Input("analysis-button", "n_clicks"),
prevent_initial_call=True,
)
def update_output_data(
n_clicks: bool
):
find_all_paths_res = dask_client.submit(find_all_paths, 0, 3)
futures[find_all_paths_res.key] = find_all_paths_res
return True, "Napping...", find_all_paths_res.key, -1
@app.callback(
[
Output("analysis-button", "disabled"),
Output("analysis-button", "children"),
Output("results", "children"),
Output("poller", "max_intervals"),
],
[Input("poller", "n_intervals")],
[State("result-tuple", "data")],
prevent_initial_call=True,
)
def poll_result(n_intervals, data):
if not data:
raise PreventUpdate()
future = futures[data]
if 'finished' not in future.status:
raise PreventUpdate()
content_data = future.result()
return (
False,
"Take a nap",
content_data[0][1],
0
)
pathfinder.py
import networkx as nx
import time
def find_all_paths(inp_source, inp_target):
G = nx.complete_graph(4) # In real program this is a much larger graph with nodes and edges (~36000 rows)
paths = []
for path in nx.all_simple_paths(G, source=inp_source, target=inp_target):
paths.append(path)
time.sleep(2)
return paths
requirements.txt
Brotli==1.0.9
click==8.0.4
cloudpickle==2.0.0
dash==2.2.0
dash-bootstrap-components==1.0.3
dash-core-components==2.0.0
dash-extensions==0.0.71
dash-html-components==2.0.0
dash-table==5.0.0
dask==2022.2.1
distributed==2022.2.1
EditorConfig==0.12.3
Flask==2.0.3
Flask-Caching==1.10.1
Flask-Compress==1.11
fsspec==2022.2.0
gunicorn==20.1.0
HeapDict==1.0.1
itsdangerous==2.1.1
Jinja2==3.0.3
jsbeautifier==1.14.0
locket==0.2.1
MarkupSafe==2.1.0
more-itertools==8.12.0
msgpack==1.0.3
networkx==2.7.1
packaging==21.3
partd==1.2.0
plotly==5.6.0
psutil==5.9.0
pyparsing==3.0.7
PyYAML==6.0
six==1.16.0
sortedcontainers==2.4.0
tblib==1.7.0
tenacity==8.0.1
toolz==0.11.2
tornado==6.1
Werkzeug==2.0.3
zict==2.1.0
When I run from the cmd line:
$ python index.py
The code runs and it works fine. However if I try to run it with Gunicorn like so:
$ gunicorn index:server
I get the error message:
Traceback (most recent call last):
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/flask/app.py", line 2073, in wsgi_app
response = self.full_dispatch_request()
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/flask/app.py", line 1511, in full_dispatch_request
self.try_trigger_before_first_request_functions()
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/flask/app.py", line 1563, in try_trigger_before_first_request_functions
self.ensure_sync(func)()
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/dash_extensions/enrich.py", line 113, in _setup_server
super()._setup_server()
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/dash/dash.py", line 1361, in _setup_server
_validate.validate_layout(self.layout, self._layout_value())
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/dash_extensions/enrich.py", line 103, in _layout_value
layout = transform.layout(layout, self._layout_is_function)
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/dash_extensions/enrich.py", line 215, in layout
self.transform_layout(layout)
File "/home/myuser/analyzer/env/lib/python3.8/site-packages/dash_extensions/enrich.py", line 668, in transform_layout
target.children = _as_list(target.children) + proxies
AttributeError: 'NoneType' object has no attribute 'children'
This issue was not occurring when I did not include the dask.distributed client. Which makes me think that my code inside the if __name__ == "__main__" will only be run when index.py is used as the entry point to the program. But I am still unsure on how to resolve the issue, can someone give some insight as to the logic behind it?
UPDATE: As commented by @Michael Delgado, I have provided a working example of what my program wants to achieve. I poll the result of the future from another callback within dash from the dash distributed future.
After some reading around my understanding is that when I run python index.py the reason it is working is because that if __name__ == '__main__' block will be the entry point, where as if I run it from gunicorn it is importing server (which is app.server) from application and not running the code from the if __name__ == '__main__'. So my program is not actually running. But I am still unsure how to resolve this issue.
