def _safe_toposort(data):
 if (len(data) == 0):
  return
 t = _toposort(data)
 while True:
  try:
   value = next(t)
   (yield value)
  except ValueError as err:
   log.debug(err.args[0])
   if (not data):
    return
   (yield pop_key(data))
   t = _toposort(data)
   continue
  except StopIteration:
   return

def _safe_toposort ( data ) : if ( len ( data ) == 0 ) : return t = _toposort ( data ) while True : try : value = next ( t ) ( yield value ) except ValueError as err : log . debug ( err . args [ 0 ] ) if ( not data ) : return ( yield pop_key ( data ) ) t = _toposort ( data ) continue except StopIteration : return
dependencies are expressed as a dictionary whose keys are items and whose values are a set of dependent items .