Also, it would be useful if you post an entire example (including your view setup and present) so we're are not debugging something more basic.

When posting code in the forum, first tap the </> symbol that appears at the top of the text entry area. Then paste code you copied from the pythonista editor between the triple backticls. That way autocorrect doesn't try to change caps or indents..

@ccc , sorry for not being clear. It goes into the pyui file. Screenshot, below. Sorry, I left it full screen so it's clear to others also.

Edit: oops, that is creating a dynamic attr in pic. But it's the same place / same idea.

The eval is called on the CustomAtrributes, in the ui.py function _view_from_dict

Sorry a few edits: I rushed this. But the self.sayhello(1,2) evals() to calling a method of that name in our class. You can leave off the self and call a function, but I think from memory you have to return True, otherwise warnings are printed.
This seems very close to what the action method does , when it's defined inside the pyui file.