code: def from_source(source_name):
          
          meta_bucket = 'net-mozaws-prod-us-west-2-pipeline-metadata'
          store = S3Store(meta_bucket)
  
          try:
              source = json.loads(store.get_key('sources.json').read().decode('utf-8'))[source_name]
          except KeyError:
              raise Exception('Unknown source {}'.format(source_name))
  
          schema = store.get_key('{}/schema.json'.format(source['metadata_prefix'])).read().decode('utf-8')
          dimensions = [f['field_name'] for f in json.loads(schema)['dimensions']]
          return Dataset(source['bucket'], dimensions, prefix=source['prefix'])
docs: Create a Dataset configured for the given source_name
  
          This is particularly convenient when the user doesn't know
          the list of dimensions or the bucket name, but only the source name.
  
          Usage example::
  
              records = Dataset.from_source('telemetry').where(
                  docType='main',
                  submissionDate='20160701',
                  appUpdateChannel='nightly'
              )