An empty list, and a missing page

A how-to guide: a menu with nothing in it explains itself; a page that is not there returns None, and the session says so without moving the reader.

from sextile import Page, PageRequest, PageRouter, Sextile, menu_page

router = PageRouter()


@router.page("1", name="inbox", title="Inbox")
async def inbox(request: PageRequest) -> Page:
    messages: list[str] = []  # none today
    return menu_page(
        request,
        items=[],
        empty=["No messages.", "", "Nothing has come in yet."],
    )


app = Sextile(name="Mail", pages=[*router])

 INBOX                                1a
  
No messages.                            
                                        
Nothing has come in yet.                
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
  
 0 index                                

An empty menu on a service that answers slowly reads as a fault unless it says otherwise, so menu_page(empty=[...]) draws the reason where the entries would go — a string for one row, a sequence for several.

A page that could exist but does not — a message the archive has not got — is a different thing. Return None, and the session shows the service’s not-found notice and leaves the reader where they were; do not draw a blank page that looks like the message. Keying *7#, a page this service has not got, shows the notice over the inbox — the reader’s next key works from the inbox still:

 UNKNOWN PAGE                           
                                        
*7# is NOT a page here.                 
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        
                                        

Why a missing page returns None rather than a notice, and how that differs from a page that failed, is in Design decisions. Give the not-found notice the service’s own words with Customise the not-found and failed notices.