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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_lists(model_class, name, bases, attrs):
 """Stores the list fields descriptors of a model."""

    model_class._lists = {}
    for k, v in attrs.iteritems():
        if isinstance(v, ListField):
            model_class._lists[k] = v
            v.name = v.name or k