Fixes 'AttributeError' when layout is a function that returns a list of components in dash layout setter

[martian0x80]

Fixes #2905
Changes as the proposed solution suggested, layout setter throws an AttributeError when layout is a function that returns a list of components. The solution checks if the layout_value is an instance of list or tuple, if it is, it wraps it in a html.Div component, otherwise proceeds as usual.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Handle the case when layout is a function that returns a list of components
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[T4rk1n]

@alexcjohnson I see this comment from a couple years ago mention this fix is mostly to empty out children for Python 2. I don't see any other uses, think we can remove the simple_clone function ?

[alexcjohnson]

@alexcjohnson I see this comment from a couple years ago mention this fix is mostly to empty out children for Python 2. I don't see any other uses, think we can remove the simple_clone function ?

We certainly don’t need to be maintaining any py2 code anymore, so yeah I think you’re right, let’s remove it.

[T4rk1n]

We can delete the function simple_clone and assign the self.validation_layout = layout_value instead.

[martian0x80]

thanks, will make requested changes

[martian0x80]

done

[T4rk1n]

Looks good, seems like there is some formatting error to fix (npm run format) then we can merge 🎉

[martian0x80]

@T4rk1n

Should I commit the other files that were formatted as well?
I avoided the commit hooks that invoke the black formatter with --no-verify because it wouldn't let me commit since other files that I did not change had formatting problems. After running npm run format, should I commit all the format changes or just the dash.py?

These are the changes.

[T4rk1n]

Should I commit the other files that were formatted as well?

No, I don't think it should have formatted all those files. npm probably took the wrong version of black, make sure the venv is activated before running npm run format as it may takes the black from a global env.

[T4rk1n]

💃 Look good, thank you.

[martian0x80]

Should I commit the other files that were formatted as well?

No, I don't think it should have formatted all those files. npm probably took the wrong version of black, make sure the venv is activated before running npm run format as it may takes the black from a global env.

Thanks, that was indeed the problem. Sorry, for being clueless.