def check_tower (self):
"""Check whether several elements can make a tower."""
for slots in (self.front_slots, self.back_slots):
if slots[0].pawn is not None and slots[1].pawn is not None:
assert slots[0].pawn.kind != 'tower'
tower = RoundObstacle (100, 1)
tower.kind = 'tower'
tower.tower = [ slots[0].pawn, slots[1].pawn ]
slots[0].pawn, slots[1].pawn = tower, None
self.table.add_pawn (tower)
if slots[0].pawn is not None and slots[0].pawn.kind == 'tower' \
and slots[2].pawn and slots[2].door_motor.angle:
slots[0].pawn.tower.append (slots[2].pawn)
slots[2].pawn = None
if slots[0].pawn is None and slots[1].pawn is None \
and slots[2].pawn and slots[2].door_motor.angle:
slots[0].pawn, slots[2].pawn = slots[2].pawn, None
