Layout as list of components does not work when layout is a function #2905
Closed
Description
Describe your context
dash 2.17.1
dash_ag_grid 31.2.0
dash-bootstrap-components 1.6.0
dash-core-components 2.0.0
dash-html-components 2.0.0
dash-mantine-components 0.12.1
dash-table 5.0.0
dash-testing-stub 0.0.2
Describe the bug
#2795 enabled you to pass a list of components to app.layout. However, this does not work when app.layout is set to a function:
import datetime
from dash import Dash, html
def layout():
return [html.H1(datetime.datetime.now())]
app = Dash(__name__)
app.layout = layout
app.run()
Gives:
Traceback (most recent call last):
File "/Users/antony_milne/Library/Application Support/JetBrains/PyCharm2024.1/scratches/scratch_51.py", line 11, in <module>
app.layout = layout
^^^^^^^^^^
File "/Users/antony_milne/Library/Application Support/hatch/env/virtual/vizro/fm3ubPZu/vizro/lib/python3.11/site-packages/dash/dash.py", line 734, in layout
[simple_clone(c) for c in layout_value._traverse_ids()],
^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'list' object has no attribute '_traverse_ids'
I see that the main motivation for #2795 was that it simplified examples for beginners, so this is not such an important case because using a function for layout is already more advanced. But still I think this should probably work.
The root of the problem is that the code in Dash.layout that handles the case that layout is a function still expect it to return a single Dash component. One possible fix would be to alter this line:
Line 729 in bbd013c
This expects a single Dash component to be returned rather than a list so it works if you just wrap it in an
html.Div.