docs: def keys_to_datetime(obj, *keys):
      """ Converts all the keys in an object to DateTime instances.
  
          Args:
              obj (dict): the JSON-like ``dict`` object to modify inplace.
              keys (str): keys of the object being converted into DateTime
                  instances.
  
          Returns:
              dict: ``obj`` inplace.
  
          >>> keys_to_datetime(None) is None
          True
          >>> keys_to_datetime({})
          {}
          >>> a = {}
          >>> id(keys_to_datetime(a)) == id(a)
          True
          >>> a = {'one': '2016-06-06T19:41:43.039284',
                   'two': '2016-06-06T19:41:43.039284'}
          >>> keys_to_datetime(a) == a
          True
          >>> keys_to_datetime(a, 'one')['one']
          datetime.datetime(2016, 6, 6, 19, 41, 43, 39284)
          >>> keys_to_datetime(a, 'one')['two']
          '2016-06-06T19:41:43.039284'
      """
      if not keys:
          return obj
      for k in keys:
          if k not in obj:
              continue
          v = obj[k]
          if not isinstance(v, string_types):
              continue
          obj[k] = parse_datetime(v)
      return obj