Initializes the class with the given data. Used by __init__.

def _initialize_attributes(self, data):
    """Initializes the class with the given data. Used by __init__."""
    attrs = dict(self.attrs)

    if self.primary_key_name is None:
      pass
    elif isinstance(self.primary_key_name, str):
      if self.primary_key_name not in attrs:
        attrs[self.primary_key_name] = None
    else:
      for pkey in self.primary_key_name:
        if pkey not in attrs:
          attrs[pkey] = None

    if self.timestamps:
      for ts_name in self.timestamps:
        if ts_name is not None and ts_name not in attrs:
          attrs[ts_name] = None

    for attr_name in attrs:
      setattr(self, attr_name, get_value(data, attr_name, attrs[attr_name]))