def TSKVsPartGetStartSector(tsk_vs_part):
  """Retrieves the start sector of a TSK volume system part object.

  Args:
    tsk_vs_part: a TSK volume system part object (instance of
                 pytsk3.TSK_VS_PART_INFO).

  Returns:
    The start sector or None.
  """
  # Note that because pytsk3.TSK_VS_PART_INFO does not explicitly defines
  # start we need to check if the attribute exists.
  return getattr(tsk_vs_part, u'start', None)