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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _init_go_sources(self, go_sources_arg, go2obj_arg):
 """Return GO sources which are present in GODag."""

        gos_user = set(go_sources_arg)
        if 'children' in self.kws and self.kws['children']:
            gos_user |= get_leaf_children(gos_user, go2obj_arg)
        gos_godag = set(go2obj_arg)
        gos_source = gos_user.intersection(gos_godag)
        gos_missing = gos_user.difference(gos_godag)
        if not gos_missing:
            return gos_source
        sys.stdout.write("{N} GO IDs NOT FOUND IN GO DAG: {GOs}\n".format(
            N=len(gos_missing), GOs=" ".join([str(e) for e in gos_missing])))
        return gos_source