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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 validate_attr(resource_attr_id, scenario_id, template_id=None):
 """ Check that a resource attribute satisfies the requirements of all the types of the resource. """

    rs = db.DBSession.query(ResourceScenario).\
                        filter(ResourceScenario.resource_attr_id==resource_attr_id,
        ResourceScenario.scenario_id==scenario_id).options(
        joinedload_all("resourceattr")).options(
        joinedload_all("dataset")
        ).one()

    error = None

    try:
        _do_validate_resourcescenario(rs, template_id)
    except HydraError as e:

        error = JSONObject(dict(
                 ref_key = rs.resourceattr.ref_key,
                 ref_id  = rs.resourceattr.get_resource_id(),
                 ref_name = rs.resourceattr.get_resource().get_name(),
                 resource_attr_id = rs.resource_attr_id,
                 attr_id          = rs.resourceattr.attr.id,
                 attr_name        = rs.resourceattr.attr.name,
                 dataset_id       = rs.dataset_id,
                 scenario_id=scenario_id,
                 template_id=template_id,
                 error_text=e.args[0]))
    return error