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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 stack_template_url(bucket_name, blueprint, endpoint):
 """Produces an s3 url for a given blueprint. Args: bucket_name (string):
 The name of the S3 bucket where the resulting templates are stored. blueprint (:class:`stacker.blueprints.base.Blueprint`):
 The blueprint object to create the URL to. endpoint (string):
 The s3 endpoint used for the bucket. Returns: string: S3 URL. """

    key_name = stack_template_key_name(blueprint)
    return "%s/%s/%s" % (endpoint, bucket_name, key_name)