I'm trying to create a module to restrict access to Cost Price in the Procurement tab of the Product view. I want to let only Administrator and Purchase Manager see the Cost Price and make the other groups cannot see the Cost Price. I have created a module below. But It doesn't work. Nothing changes and everyone still can see the Cost Price. Can anybody tell me what my mistake is?

__init__.py

import product_template 

__openerp__.py

{
	"name": "Hide Cost Price from Some Groups",
	"version": "1.0.0",
	"author": "Budi Hartono",
	"depends": ["product"],
	"category": "",
	"description": """
	Hide Cost Price from Some Groups.
	""",
	"website": "http://www.recoremedia.com",
	"data": [
		"product_view.xml",
    ],
	"installable": True,
	"active": False,
}

product_template.py

from openerp.osv import fields, osv
from openerp.tools.translate import _
class product_template(osv.osv):
    _inherit = "product.template"

product_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
<data>
  <record id="product_template_form_view_restricted" model="ir.ui.view">
    <field name="name">product.template.common.form</field>
    <field name="model">product.template</field>
    <field name="inherit_id" ref="product.product_template_form_view"/>
    <field name="arch" type="xml">
      <field name="standard_price" position="replace">          
        <field name="standard_price" groups="base.group_erp_manager,purchase.group_purchase_manager"/>
      </field>
    </field>
  </record>
</data>
</openerp>