[BUG] Unsupported format string passed to Button.__format__

[ghost]

Context

dash                 1.6.0
dash-core-components 1.5.0
dash-html-components 1.0.1
dash-renderer        1.2.0
dash-table           4.5.0
dash-daq                  0.2.1
dash-bootstrap-components 0.7.2

Bug description

When I run my application, I receive following error :

Traceback (most recent call last):
File "app.py", line 452, in
@app.callback(
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\dash\dash.py", line 1264, in callback
self._validate_callback(output, inputs, state)
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\dash\dash.py", line 921, in _validate_callback
if arg_id not in layout and arg_id != layout_id:
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\dash\development\base_component.py", line 257, in iter
for t in self._traverse():
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\dash\development\base_component.py", line 217, in _traverse
for t in self._traverse_with_paths():
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\dash\development\base_component.py", line 252, in _traverse_with_paths
for p, t in i._traverse_with_paths():
File "C:\Users\user\AppData\Local\Programs\Python\Python38\lib\site-packages\dash\development\base_component.py", line 244, in _traverse_with_paths
"(id={:s})".format(i.id)
TypeError: unsupported format string passed to Button.format

The error appear on a line where I define this callback :

@app.callback(
    Output('reportPid', 'data'),
    [Input('report1Button', 'n_clicks')],
    [State('pid1', 'data')]
)
def report1(n, data):
    return data

---

The error seems to be about naming of one of my button.

The weird thing is, if I remove this callback, no error.
I must be doing something wrong in this callback but I cannot see what, and the error is not helpful...

[alexcjohnson]

I suspect somewhere in your layout you have a set of children that should be wrapped in an array and the second one is a Button - ie
html.Div(Something(...), Button(...), ...)
should be
html.Div([Something(...), Button(...), ...])
(isn't necessarily a Div but you get the point)

This is only showing up during callback definition because that's the first place we walk the layout tree.

I'm starting to think a v2 component API should only accept arrays for children... otherwise it's super tricky for us to figure out how to give a more helpful error for this case.

[ghost]

Awesome !

That's exactly it !
Thank you very much for the hint, I would never have found by myself...

Thanks again for the saved time !