I want to inherit the existing sale module in to my new custom module which extends current sale module and adds a serial number column to my sale order line tree. But it throws an error like as follows , where am i went wrong ?
 File "parser.pxi", line 1468, in lxml.etree._parseDocFromFilelike (src/lxml/lxml.etree.c:81783)
 File "parser.pxi", line 1024, in lxml.etree._BaseParser._parseDocFromFilelike (src/lxml/lxml.etree.c:78830)
 File "parser.pxi", line 569, in lxml.etree._ParserContext._handleParseResultDoc (src/lxml/lxml.etree.c:74567)
 File "parser.pxi", line 650, in lxml.etree._handleParseResult (src/lxml/lxml.etree.c:75458)
 File "parser.pxi", line 590, in lxml.etree._raiseParseError (src/lxml/lxml.etree.c:74791)
 XMLSyntaxError: AttValue: " or ' expected, line 31, column 28
view.py
        <record id="view_order_line_tree2" model="ir.ui.view">
        <field name="name">sale.order.line.tree.inherit</field>
        <field name="model">sale.order.line</field>
        <field name="inherit_id" ref=sale.view_order_form/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='order_line']/tree" position="attributes">
                <attribute name="sl_no"/>
            </xpath>
        </field>
       </record>
sale_modified.py file contents
    class sale_order_line2(osv.osv):
            _inherit = 'sale.order.line'
           _columns = {
              'sl_no': fields.integer("SL No", required=True)
                  }
             _defaults = {
                  'sl_no':1,
                   }
Any hint to solve the above mentioned issue is appreciated .. Thanks in advance
 
                        
Sale Order Serial Numbers & Product Images | Auto Numbering & Custom Images in Reports in Odoo
This Odoo module automatically assigns serial numbers to sale order lines and displays product images in reports. If a serial number is manually set to a custom string (e.g., "A"), the next item resets numbering to 1. Additionally, if a product has no image, you can manually upload a custom image for the sale order line—without affecting the original product image.
https://apps.odoo.com/apps/modules/18.0/mh_display_serial_number_and_image