Sometimes users make mistakes, and they realize it after delivering it. 

So i choosed the follwing process to do the reverse picking process :

Make an automatic return, by creating reverse stock move, for example if I deliver a quantity to a client, source would be "mystock" and destination would be "client location", so the follwing method will create a reverse stock move from the "client locations" to "mystock", and the confirm this stock move, and it will be on the done state.

Here after the methode suggested : 

class StockPickingOut(orm.Model):

    _inherit = 'stock.picking.out'
    _name = 'stock.picking.out'

   

def cancel_delivery(self, cr, uid, ids, context=None):

        move_pool = self.pool.get('account.move')
        stock_pool = self.pool.get('stock.move')
        date_cur = time.strftime('%Y-%m-%d %H:%M:%S')
        uom_obj = self.pool.get('product.uom')
        wf_service = netsvc.LocalService("workflow")
        moves = []
        for delivery in self.browse(cr,uid,ids,context):

            for move_line in delivery.move_lines:
                # changer l etat
                stock_pool.write(cr, uid, move_line.id, {'state':'draft'})
                # creer mouvement inverse
                new_location = move_line.location_dest_id.id
                new_move=stock_pool.copy(cr, uid, move_line.id, {
                                            'picking_id': '',
                                            'partner_id': '',
                                            'type': 'in',
                                            'product_qty': move_line.product_qty,
                                            'product_uos_qty': uom_obj._compute_qty(cr, uid, move_line.product_uom.id, move_line.product_qty, move_line.product_uos.id),
                                            'state': 'draft',
                                            'location_id': new_location,
                                            'location_dest_id': move_line.location_id.id,
                                            'date': date_cur,
                })
                #valider mouvement inverse
                moves.append(new_move)
        stock_pool.action_done(cr,uid,moves)
        self.write(cr,uid,ids,{'state':'confirmed'})
        return True

The problem is when I verify the returned quantities to mystock,  i found that the last line of stock move is returned twice, I don't know why. For example if I expect for 3 products the following returned quantities : 

P1 : Q1/ P2: Q2 / P3: Q3  I'm getting : P1 : Q1/ P2: Q2 / P3: Q3*2      The problem is always with the last line of the stock move lines.

I'll post here the action_done method, maybe you'll find the solution : 

    def action_done(self, cr, uid, ids, context=None):
        """ Makes the move done and if all moves are done, it will finish the picking.
        @return:
        """
        picking_ids = []
        move_ids = []
        wf_service = netsvc.LocalService("workflow")
        if context is None:
            context = {}

        todo = []
        for move in self.browse(cr, uid, ids, context=context):
            if move.state=="draft":
                todo.append(move.id)
        if todo:
            self.action_confirm(cr, uid, todo, context=context)
            todo = []

        for move in self.browse(cr, uid, ids, context=context):
            if move.state in ['done','cancel']:
                continue
            move_ids.append(move.id)

            if move.picking_id:
                picking_ids.append(move.picking_id.id)
            if move.move_dest_id.id and (move.state != 'done'):
                # Downstream move should only be triggered if this move is the last pending upstream move
                other_upstream_move_ids = self.search(cr, uid, [('id','!=',move.id),('state','not in',['done','cancel']),
                                            ('move_dest_id','=',move.move_dest_id.id)], context=context)
                if not other_upstream_move_ids:
                    self.write(cr, uid, [move.id], {'move_history_ids': [(4, move.move_dest_id.id)]})
                    if move.move_dest_id.state in ('waiting', 'confirmed'):
                        self.force_assign(cr, uid, [move.move_dest_id.id], context=context)
                        if move.move_dest_id.picking_id:
                            wf_service.trg_write(uid, 'stock.picking', move.move_dest_id.picking_id.id, cr)
                        if move.move_dest_id.auto_validate:
                            self.action_done(cr, uid, [move.move_dest_id.id], context=context)

            self._create_product_valuation_moves(cr, uid, move, context=context)
            if move.state not in ('confirmed','done','assigned'):
                todo.append(move.id)

        if todo:
            self.action_confirm(cr, uid, todo, context=context)

        self.write(cr, uid, move_ids, {'state': 'done', 'date': time.strftime(DEFAULT_SERVER_DATETIME_FORMAT)}, context=context)
        for id in move_ids:
            wf_service.trg_trigger(uid, 'stock.move', id, cr)

        for pick_id in picking_ids:
            wf_service.trg_write(uid, 'stock.picking', pick_id, cr)

        return True

Any suggestions will be welcome.

Thanks.