@Hilar AK: regarding to your answer i trief the following (mostly copied from oribinal sale_views.xml:

<record id="x_view_order_line_tree" model="ir.ui.view">
    <field name="name">sale.order.line.tree</field>
    <field name="model">sale.order.line</field>
    <field name="arch" type="xml">
        <tree string="Sales Order Lines" create="false">
            <field name="order_id"/>
            <field name="order_partner_id"/>
            <field name="name"/>
            <field name="salesman_id"/>
            <field name="product_uom_qty" string="Qty"/>
            <field name="qty_delivered"/>
            <field name="qty_invoiced"/>
            <field name="qty_to_invoice"/>
            <field name="product_uom" string="Unit of Measure" groups="uom.group_uom"/>
            <field name="price_subtotal" sum="Total" widget="monetary"/>
        </tree>
    </field>
</record>
<record id="x_sale_order_line_view_form_readonly" model="ir.ui.view">
    <field name="name">sale.order.line.form.readonly</field>
    <field name="model">sale.order.line</field>
    <field name="arch" type="xml">
        <form string="Sales Order Item">
            <sheet>
                <div class="oe_title">
                    <h1>
                        <field name="display_name" readonly="1"/>
                    </h1>
                </div>
                <group>
                    <group>
                        <field name="order_id" readonly="1"/>
                        <field name="product_id" readonly="1"/>
                        <field name="name" readonly="1"/>
                        <field name="product_uom_qty" readonly="1"/>
                        <field name="qty_delivered" readonly="1"/>
                        <field name="qty_invoiced"/>
                        <field name="product_uom" readonly="1"/>
                        <field name="company_id" options="{'no_create': True}" groups="base.group_multi_company"/>
                        <field name="order_partner_id" invisible="1"/>
                        <field name="display_type" invisible="1"/>
                        <field name="product_updatable" invisible="1"/>
                    </group>
                    <group>
                        <field name="price_unit" readonly="1"/>
                        <field name="discount" groups="sale.group_discount_per_so_line" readonly="1"/>
                        <field name="price_subtotal" widget="monetary"/>
                        <field name="tax_id" widget="many2many_tags" readonly="1"/>
                        <field name="price_tax" widget="monetary"/>
                        <field name="price_total" widget="monetary"/>
                        <field name="currency_id" invisible="1"/>
                    </group>
                </group>
            </sheet>
        </form>
    </field>
</record>
<record id="x_view_sales_order_line_filter" model="ir.ui.view">
    <field name="name">sale.order.line.select</field>
    <field name="model">sale.order.line</field>
    <field name="arch" type="xml">
        <search string="Search Sales Order">
            <filter string="To Invoice" name="to_invoice" domain="[('qty_to_invoice','!=', 0)]"  help="Sales Order Lines ready to be invoiced"/>
            <separator/>
            <filter string="My Sales Order Lines" name="my_sales_order_lines" domain="[('salesman_id','=',uid)]" help="Sales Order Lines related to a Sales Order of mine"/>
            <field name="order_id"/>
            <field name="order_partner_id" operator="child_of"/>
            <field name="product_id"/>
            <field name="salesman_id"/>
            <group expand="0" string="Group By">
                <filter string="Product" name="product" domain="[]" context="{'group_by':'product_id'}"/>
                <filter string="Order" name="order" domain="[]" context="{'group_by':'order_id'}"/>
                <filter string="Salesperson" name="salesperson" domain="[]" context="{'group_by':'salesman_id'}"/>
            </group>
        </search>
    </field>
</record>
<record id="x_action_sale_lines_custom" model="ir.actions.act_window">
    <field name="name">Sales Order Lines</field>
    <field name="type">ir.actions.act_window</field>
    <field name="res_model">sale.order.line</field>
    <field name="view_type">form</field>
    <field name="view_mode">tree,form</field>
    <field name="search_view_id" ref="x_article.x_view_sales_order_line_filter"/>
    <field name="domain"></field>
    <field name="context">{
            'search_default_team_id': [active_id],
        }
    </field>
</record>
<record id="x_sale_order_action_view_order_tree" model="ir.actions.act_window.view">
    <field name="sequence" eval="1"/>
    <field name="view_mode">tree</field>
    <field name="view_id" ref="x_article.x_view_order_line_tree"/>
    <field name="act_window_id" ref="x_action_sale_lines_custom"/>
</record>

But what should i return in python code now?

You need to define your action as XML in views file and need to bind your views with actions. Then after fetch the actions data from your custom functions and return as like you done. 

This is the format of binding new actions with views.

eg:

<record id="action_auto_backup_odoo_config_view_form_bind" model="ir.actions.act_window.view">
    <field eval="2" name="sequence"/>
    <field name="view_mode">form</field>
    <field name="view_id" ref="view_auto_backup_config_form"/>
    <field name="act_window_id" ref="action_auto_backup_odoo_config"/>
</record>

Here act_window_id should be your action ID.