code: def GetServiceVersions(namespace):
     
     def compare(a, b):
        if a == b:
           return 0
        if b in parentMap[a]:
           return -1
        if a in parentMap[b]:
           return 1
        return (a > b) - (a < b)
  
     if PY3:
        return sorted([v for (v, n) in iteritems(serviceNsMap) if n == namespace],
                      key=cmp_to_key(compare))
     else:
        return sorted([v for (v, n) in iteritems(serviceNsMap) if n == namespace],
                      compare)
docs: Get all the versions for the service with specified namespace (partially) ordered
     by compatibility (i.e. any version in the list that is compatible with some version
     v in the list will preceed v)