Description
openedon Nov 22, 2024
Hi everyone,
thanks for providing such a wonderful package. I had an issue and I have been cracking my head at this long enough to belief this is a bug with dash.no_update not being serializiable. While writing this issue, I found that dash.no_update is not the issue but obfusicates the real error.
Situation: Given a user picked date range, I gather data and display it. However, I want to cover the case when there simply is no data to present.
For this, I aim to not update the already presented data and instead show an alert, notifiying the user of the absence of data.
See this line (context below):
return no_update, no_update, True, dfdf is an AssertionError. Apparently, those are not serializiable by json. However, see error log at bottom, dash reports that dash.no_update seems to be the culprit.
The error below is resolved by parsing df into a string via ´str(df)´
@callback(
Output(component_id='figcontainer', component_property='figure'),
Output(component_id='table', component_property='data'),
Output(component_id="alert", component_property='is_open'),
Output(component_id="alert",component_property='children'),
Input(component_id='date_picker', component_property='start_date'),
Input(component_id='date_picker', component_property='end_date'),
)
def update_graph(start, end):
df = get_bookings_in_interval(start, end)
# if there is no data, keep previous states and use alert
if type(df) is AssertionError:
return no_update, no_update, True, df
#else simply display the information and dont update the alert
all_appointments, best_days_with_numbers, cleaning_schedule = create_dfs(df)
fig = create_figure(start, end, all_appointments, cleaning_schedule)
return fig.to_dict(), best_days_with_numbers.to_dict(orient="records"), no_update, no_update
#either returns a df or an AssertionError
def get_bookings_in_interval(start, end):
df = None
try:
data = get(#do something)
assert data.status_code == 200 , "Failed to fetch bookings"
parsed_data = dict(data.json())
assert len(parsed_data["bookings"]) > 0, "No items in Response")
#do something
except AssertionError as e:
print(e)
return e
return dataEnvironment used:
dash 2.18.2
dash-bootstrap-components 1.6.0
dash-core-components 2.0.0
dash-html-components 2.0.0
dash-table 5.0.0
Error Log:
dash.exceptions.InvalidCallbackReturnValue: The callback for `[<Output `figcontainer.figure`>, <Output `table.data`>, <Output `alert.is_open`>, <Output `alert.children`>]`
returned a value having type `NoUpdate`
which is not JSON serializable.
The value in question is either the only value returned,
or is in the top level of the returned list,
and has string representation
`<dash._callback.NoUpdate object at 0x000002A7FA5ACBE0>`
In general, Dash properties can only be
dash components, strings, dictionaries, numbers, None,
or lists of those.
Expected behavior
As dash.no_update is explicitly mentioned, I expected it to be culprit. I think the error hint should either reflect the possibility of other returned values being the issue or explicitly state the correct one.
Screenshots