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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 get_relation_graph(self, depth=None):
 """ Get all `SampleRelation`s in the relation graph of the sample. :param depth: max depth of the returned graph. None retrieves the complete graph. :return: An iterator over the relations """

        url = '{}relation_graph/'.format(self.url)
        if depth is not None:
            params = {'depth': depth}
        else:
            params = {}

        from .sample_relation import SampleRelation
        return SampleRelation._get_iter_from_url(url, params=params, append_base_url=False)