docs: def valueof(records, key):
      """Extract the value corresponding to the given key in all the dictionaries
  
      >>> bands = [{'name': 'Led Zeppelin', 'singer': 'Robert Plant', 'guitarist': 'Jimmy Page'},
      ... {'name': 'Metallica', 'singer': 'James Hetfield', 'guitarist': 'Kirk Hammet'}]
      >>> valueof(bands, 'singer')
      ['Robert Plant', 'James Hetfield']
  
      """
      if isinstance(records, dict):
          records = [records]
      return map(operator.itemgetter(key), records)