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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 by_id(cls, semantictag_id, autoflush=True):
		'''Return the semantic tag with the given id, or None.

		:param semantictag_id: the id of the semantic tag to return
		:type semantictag_id: string

		:returns: the semantic tag with the given id, or None if there is no tag with
			that id
		:rtype: ckan.model.semantictag.SemanticTag # TODO check this

		'''
		query = meta.Session.query(SemanticTag).filter(SemanticTag.id==semantictag_id)
		query = query.autoflush(autoflush)
		semantictag = query.first()
		return semantictag