#NEWLINE# def GetVolumeIdentifiers( self , volume_system ) : #NEWLINE# #INDENT# 'Retrieves the volume identifiers.\n\n    Args:\n      volume_system: The volume system (instance of dfvfs.VolumeSystem).\n\n    Returns:\n      A sorted list containing the volume identifiers.\n    ' #NEWLINE# volume_identifiers = [ ] #NEWLINE# for volume in volume_system . volumes : #NEWLINE# #INDENT# volume_identifier = getattr ( volume , 'identifier' , None ) #NEWLINE# if volume_identifier : #NEWLINE# #INDENT# volume_identifiers . append ( volume_identifier ) #NEWLINE# #UNINDENT# #UNINDENT# return sorted ( volume_system )