Tkinter: closing a popup menu by clicking elsewhere

[Peter Otten]

How can I close a popup menu in Tkinter by clicking elsewhere on the
toplevel window underneath? 

I tried popup.grab_set() but this causes the popup to close immediately.

An alternative would be 

def hidepopup(event=None):
    popup.unpost()
    return "break"

root.bind_all("<Button-1>", hidepopup)

but I'd then need a way to make sure that other bindings in children are not
processed or only processed after hidepopup. 

Any hints welcome,
Peter