Can message handlers be private?

[dAnjou]

Hi,

I saw these two methods in DirectoryTree:

textual/src/textual/widgets/_directory_tree.py

Line 427 in 4d1f057

def _on_tree_node_expanded(self, event: Tree.NodeExpanded) -> None:

textual/src/textual/widgets/_directory_tree.py

Line 437 in 4d1f057

def _on_tree_node_selected(self, event: Tree.NodeSelected) -> None:

Both are not overrides of Tree methods, and they are not called anywhere. Which makes me think that message handlers can be private. But it's not documented, for example here:

https://textual.textualize.io/guide/events/#handler-naming
https://textual.textualize.io/widgets/tree/#messages

Is there any difference between prefixing handlers with on_ or _on_? And can you elaborate whether others should consider using _on_?

Thanks 🙏

[willmcgugan]

They can indeed be private. This was to allow widgets in the code library to define handlers, without forcing subclasses to stick to the same signature.