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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 save_kb_dyn_config(kb_id, field, expression, collection=None):
 """Save a dynamic knowledge base configuration. :param kb_id: the id :param field: the field where values are extracted :param expression: ..using this expression :param collection: ..in a certain collection (default is all) """

    # check that collection exists
    if collection:
        collection = Collection.query.filter_by(name=collection).one()

    kb = get_kb_by_id(kb_id)
    kb.set_dyn_config(field, expression, collection)