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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 _initialize_references(model_class, name, bases, attrs):
 """Stores the list of reference field descriptors of a model."""

    model_class._references = {}
    h = {}
    deferred = []
    for k, v in attrs.iteritems():
        if isinstance(v, ReferenceField):
            model_class._references[k] = v
            v.name = v.name or k
            att = Attribute(name=v.attname)
            h[v.attname] = att
            setattr(model_class, v.attname, att)
            refd = _initialize_referenced(model_class, v)
            if refd:
                deferred.append(refd)
    attrs.update(h)
    return deferred