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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 root(self):
 """Reference to the `Schema` that this field belongs to even if it is buried in a `List`. Return `None` for unbound fields. """

        ret = self
        while hasattr(ret, 'parent') and ret.parent:
            ret = ret.parent
        return ret if isinstance(ret, SchemaABC) else None