Attach file before save

hi community ,
i’m trying to upload a picture or file before saving the doctype ,
i have this scenario:

  1. save the pic to my public/files , with a name i made unique (

  2. make new file and pass the name to it.
    attach_image = frappe.get_doc({
    “doctype”: “File”,
    “file_name”: name,
    “file_url”: path + name,

  3. set the path to the attach image after_insert with update database .
    def after_insert(self):
    img_path = “/files/” + + “.png”

     frappe.db.sql("""update `tabSlash` set barcode = %s
         where name = %s""", (img_path,

(1)step is the problem
for now i can do it if put the pictures manually to public/files folder

i wonder if there is a way to put file to public/file folder when the doctype is not save yet !