I’ve made a few Dash applications now and I’ve loved it a lot. Generally I’m happy to write my own frameworks to drive Dash to get my own very specific needs working, but there are a few general sore points as a Python developer that I wanted to give feedback on.
Please take this as what it is, just my viewpoints coming from a very Python heavy background, I hope that’s useful to you but if not please ignore. All of these I can and do workaround, but I really feel if they were fixed it would make for a better Dash.
- Type Checking OR Type Hinting
All 3 of these are accepted (i.e. won’t throw an exception):
html.Div(html.Div()) html.Div([html.Div(), html.Div()]) html.Div(html.Div(), html.Div())
I appreciate that you want to make people’s code easier and less verbose so for the case where
children is a single element, though this is an inconsistent with the
state argument in a callback, but this makes it very easy to write the third example which results in this:
Which at no point throws an exception, and because there is no type hinting either then PyCharm and MyPy don’t have a chance to point to this as possible problem.
- Multiple Callbacks with Output to the same Prop
Particularly with the new DataTable it’s really useful to have multiple Inputs both Output to a DataTable. The “Timestamp” solution to work out which Input triggered isn’t available for every possible Input and even when it is >2 Timestamps turns in to a spaghetti monster. I would be happy to handle the state carefully myself in code like this:
@app.callback(output=Output(*foo_prop), inputs=[Input(*bar_prop)], state=[State(*baz_prop)]): def my_func1: pass @app.callback(output=Output(*foo_prop), inputs=[Input(*baz_prop)], state=[State(*bar_prop)]): def my_func2: pass
- Circular References
Firstly this doesn’t even throw a Python exception (last I checked, I know there’s an issue on this) which is annoying, but even if it did there are times when I would want to override it sometimes. I’m coming across situations where if propA is updated then I want propB to be updated, and if propB is updated I want propA to be updated, in this case I would put a check in to raise PreventUpdate when they don’t need updating.
- Clean-support for multi-page apps with callback checking kept
So I know this can be done by creating multiple Dash Apps and using the same Flask Server and using “url_base_pathname”, but this isn’t explained in the documentation and it just feels a little odd. Maybe this one isn’t that important, but it just doesn’t feel nearly as magical as the rest of Dash
- Stuff I know is getting fixed in the future but still deserve to be on this list:
a. Removing None Callbacks on Page-Load
b. Output to multiple Props
Both will make a big difference to both performance and creating a cleaner layout to my applications.