Return a list of nodes in fdefs that have no inbound edges

def getStartNodes(fdefs,calls):
    '''Return a list of nodes in fdefs that have no inbound edges'''
    s=[]
    for source in fdefs:
        for fn in fdefs[source]:
            inboundEdges=False
            for call in calls:
                if call.target==fn:
                    inboundEdges=True
            if not inboundEdges:
                s.append(fn)
    return s