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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 sharded_cluster_link(rel, cluster_id=None, shard_id=None, router_id=None, self_rel=False):
 """Helper for getting a ShardedCluster link document, given a rel."""

    clusters_href = '/v1/sharded_clusters'
    link = _SHARDED_CLUSTER_LINKS[rel].copy()
    link['href'] = link['href'].format(**locals())
    link['rel'] = 'self' if self_rel else rel
    return link