Arguments to pass while calling python function "def function(self,cdt)" in java script

Hi,
I have written a code for Delivery Note in python and calling it at ‘validaiton’. I does some calculations base on Delivery Note Items and update values in both child doc Delivery Note Item and parent doc Delivery Note on save . I would like to know how can I call this function when I change a value in the child doc Delivery Note Item. I can not figure out the arguments to pass for self and cdt during call from javascript

For example:
Python code

def update_pipe_weight_um(self, cdt):
    estimate_weight_um_temp = 0
    total_um_temp = 0
    discount_temp = 0
    total_scale_weight_um_temp = 0
    weight_difference_um_temp = 0
    weight_difference_percentage_um_temp = 0
    has_pipe = 0,

    for d in self.items:
        if 'Pipe-MS' in str(d.item_code):
            estimate_weight_um_temp     += d.total_weight_um
            total_um_temp               += d.amount_um
            total_scale_weight_um_temp  += d.total_scale_weight_um
            has_pipe = 1

    if has_pipe == 1:
        self.total_weight_um                    = self.loaded_vehicle_weight_um - self.empty_vehicle_weight_um
        weight_difference_um_temp               = self.total_weight_um - estimate_weight_um_temp
        weight_difference_percentage_um_temp    = (weight_difference_um_temp / estimate_weight_um_temp) * 100
        discount_temp                           = self.total - total_um_temp

        self.estimate_weight_um                 = estimate_weight_um_temp
        self.total_um                           = total_um_temp
        self.weight_difference_um               = weight_difference_um_temp
        self.weight_difference_percentage_um    = weight_difference_percentage_um_temp
        self.total_scale_weight_um              = total_scale_weight_um_temp
        self.discount_amount                    = discount_temp
        self.calculate_taxes_and_totals()

Javascript code

frappe.ui.form.on("Delivery Note Item", { 
    scale_weight: function(frm,cdt,cdn){
        var item_code = frappe.model.get_doc(cdt, cdn);
        if (item_code.item_code){
            if(item_code.item_code.includes("Pipe-MS",0)){
                
                frm.call({
                    method: "steelpipes.sp_delivery_note.sp_delivery_note_item.update_pipe_weight_um",
                    args: {self: "what should i pass", cdt: "what should i pass"},
                    callback:function(r){
                        
                    } 

                })
            }
            
        }
    }
})