'setref()
Set a reference point for heap usage measurement.  This applies to
both the heap[1] and heapu[2] methods. The heap() method will only
show the objects allocated after the time setref was called. The
heapu() method, since it deals with summary data and not actual
objects, will show the difference of sizes and counts compared to when
setref was called.
References
[0] heapy_Use.html#heapykinds.Use.setref
[1] heapy_Use.html#heapykinds.Use.heap
[2] heapy_Use.html#heapykinds.Use.heapu'

def setref(self, reachable=None, unreachable=None):

    if ((reachable is None) and (unreachable is None)):
        self.setrelheap()
        self.setrelheapu()
    else:
        if (reachable is not None):
            self.setrelheap(reachable)
        if (unreachable is not None):
            self.setrelheapu(unreachable)
