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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 model_stats(self):
 """A dict mapping the model's ``default_stats`` to arrays of values. The returned array has shape ``nwalkers x niterations``. """

        stats = self.model.default_stats
        return blob_data_to_dict(stats, self._sampler.blobs)