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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_s3store_instance(bucket):
 """Return an instance of S3Store."""

    global _s3store_instances

    key = "%s" % bucket

    try:
        instance = _s3store_instances[key]
    except KeyError:
        instance = S3Store(
            bucket=bucket
        )
        _s3store_instances[key] = instance

    return instance