Hey Tessnim ZRAYGA,

May be this Will help You.

class AccountInvoice(models.Model):   
    _inherit = 'account.invoice'   

    all_due_date = fields.Char(compute= '_cal_all_due_date', string='All Due Date')      

    @api.multi   
    def _cal_all_due_date(self):      
        inv_due_date = []      
        for inv in self:         
            if inv.date_due:            
                inv_due_date.append(inv.date_due)