code: def callback(cfunc):
      
      # Note:
      # ROOT wants a c_voidp whose addressof() == the call site of the target
      # function. This hackery is necessary to achieve that.
      return C.c_voidp.from_address(C.cast(cfunc, C.c_voidp).value)
docs: Turn a ctypes CFUNCTYPE instance into a value which can be passed into PyROOT