The great OpenERP 7 directory structure mystery - centos

Question

I am currently deploying OpenERP 7 on a CentOS 6.4 machine.
I'm virtualizing the whole thing so that I can backup the whole system if I mess up.
Everything seems to be fine, I changed my models, my views, but it's been 2 days I've been banging my head against a seemingly impossible problem.
My deployment is for a book factory, so the product needed to be customized (number of pages, binding type , and so forth...)
In the new product view, I need something that can sum to fields x_colorpages and x_bwpages to populate a third field: x_totalpages. Easy huh?
I've got my XML , product.normal.form view based on the product.poduct object
When I change the value in "x_paginecolori" or "xpagineBN" it should automatically trigger the onchange function.
So I went in the product module code and coded my cal_change_event
In the python file product.py located in:
/usr/lib/python2.6/site-packages/openerp-7.0_20130524_231019-py2.6.egg/openerp/addons/account/product.py
def cal_change_event(self, cr, uid, ids, x_PagineColori, x_PagineBN):
res = {}
sum = 0
if not x_PagineColori:
return {}
else if not x_PagineBN:
return {}
else:
sum = x_PagineColori + x_PagineBN
res={'x_pagine':sum }
return {'value':res}
NO matter what i do , the onchange event will allways trigger a warning popup:
File "/usr/lib/python2.6/site-packages/openerp-7.0_20130524_231019-py2.6.egg/openerp/osv/osv.py", line 185, in execute_cr
return getattr(object, method)(cr, uid, *args, **kw)
AttributeError: 'product.product' object has no attribute 'cal_change_event'
It seems to me that the function is not seen, where should I put it?
How can Product.Product not have this attribute if I placed it in the class inside product.py?
I grep'd the whole CENTOS installation in search for multiple instances of openerp , or to see if I missed something about product.py
It seems that the product.py is not the right file, even if I erase other On_change functions, nothing bad really happens.
But the directory must be right, because the error log gives me that same location in the debug popup window.
Should I be building a custom module fron scratch to make this work? Is it forbidden somehow to modify the standard product module?
Thanks in advance for any insight, my brain is defaulting on this one.
here is my Xml:
<?xml version="1.0"?>
<form string="Product" version="7.0">
<sheet>
<div>
<label for="x_partner2" string="Cliente Referente del prodotto"/>
<field name="x_partner2" />
</div>
<field name="image_medium" widget="image" class="oe_avatar oe_left"/>
<div class="oe_title">
<div class="oe_edit_only">
<label for="name" string="Product Name"/>
</div>
<h1>
<field name="name"/>
</h1>
<label for="categ_id" class="oe_edit_only"/>
<h2><field name="categ_id"/></h2>
<div name="options" groups="base.group_user">
<field name="sale_ok"/>
<label for="sale_ok"/>
</div>
</div>
<div class="oe_right oe_button_box" name="buttons">
</div>
<notebook>
<page string="Information">
<group>
<group>
<field name="type"/>
<field name="uom_id" on_change="onchange_uom(uom_id,uom_po_id)" groups="product.group_uom"/>
<field name="list_price"/>
</group>
<group>
<field name="default_code"/>
<label for="ean13"/>
<div name="ean">
<field name="ean13" placeholder="e.g. 5901234123457"/>
</div>
</group>
<group>
<field groups="product.group_product_variant" name="variants"/>
<field name="price_margin" groups="product.group_product_variant"/>
<field name="price_extra" groups="product.group_product_variant"/>
</group>
</group>
<field name="description" placeholder="describe the product characteristics..."/>
</page>
<page string="Dati del volume Universal Book">
<group>
<group>
<field name="x_DataCreazione" />
<field name="x_DataUltimaModifica" />
<field name="x_Autore" />
<field name="x_Larghezza"/>
<field name="x_Altezza" />
<field name="x_Dorso"/>
<field name="x_Rilegatura" />
<field name="x_volumiformati" />
</group>
</group>
<group>
<field name="x_PagineColori" on_change="cal_change_event(x_PagineColori,x_PagineBN)" />
<field name="x_PagineBN" on_change="cal_change_event(x_PagineColori,x_PagineBN)" />
<field name="x_pagine" />
</group>
<group>
<field name="x_prezzo" />
</group>
</page>
<page string="Copertina">
<group>
<group>
<field name="x_TipoCartaCopertina"/>
<field name="x_TipoStampaCopertina"/>
<field name="x_TipoFFR"/>
<field name="x_PlastificazioneCopertina" />
<field name="x_NumeroCopertinePerPagina" />
</group>
<group>
<field name="x_TipoCartaSovracopertina"/>
<field name="x_TipoStampaScopertina"/>
<field name="x_TipoFFRSovracopertina"/>
<field name="x_PlastificazioneSovracopertina"/>
</group>
</group>
<label for="x_aletta" string="Libro con alette?"/>
<field name="x_aletta" />
<label for="x_Note" string="Note"/>
<field name="x_Note" />
</page>
<page string="Margini">
<group>
<field name="x_pagriferimento"/>
<field name="x_MargineDestro"/>
<field name="x_MargineDestro"/>
<field name="x_MargineInferiore" />
<field name="x_MargSinistro" />
<field name="x_MargineSuperiore"/>
<field name="x_RiferimentoLIFRE" />
<field name="x_MergineSuperioreLIFRE" />
<field name="x_MargineInferioreLIFRE" />
</group>
</page>
<page string="Procurements" groups="base.group_user">
<group name="procurement">
<group name="general">
<field name="cost_method" groups="product.group_costing_method"/>
<field name="standard_price" attrs="{'readonly':[('cost_method','=','average')]}"/>
</group>
<group name="procurement_uom" groups="product.group_uom" string="Purchase">
<field name="uom_po_id"/>
</group>
</group>
<separator string="Description for Suppliers"/>
<field name="description_purchase" placeholder="This note will be displayed on requests for quotation..."/>
</page>
<page string="Inventory" groups="base.group_user">
<group name="inventory">
<group name="status" string="Status">
<field name="state"/>
<field name="product_manager"/>
</group>
<group name="Weights" groups="product.group_stock_packaging" string="Weights">
<field digits="(14, 3)" name="volume" attrs="{'readonly':[('type','=','service')]}"/>
<field name="weight" attrs="{'readonly':[('type','=','service')]}"/>
<field name="weight_net" attrs="{'readonly':[('type','=','service')]}"/>
</group>
</group>
</page>
<page string="Sales" attrs="{'invisible':[('sale_ok','=',False)]}">
<group name="sale">
<group string="Sale Conditions">
<label for="warranty"/>
<div>
<field name="warranty" class="oe_inline"/> months
</div>
</group>
<group groups="product.group_uos" string="Unit of Measure">
<field name="uos_id"/>
<field name="uos_coeff"/>
<field name="mes_type"/>
</group>
</group>
<field name="packaging" groups="product.group_stock_packaging">
<form string="Packaging" version="7.0">
<group col="4">
<field name="ean"/>
<field name="sequence" invisible="1"/>
<newline/>
<field name="qty"/>
<field name="ul"/>
<field name="weight_ul"/>
<separator colspan="4" string="Palletization"/>
<field name="ul_qty"/>
<field name="rows"/>
<field name="weight"/>
<separator colspan="4" string="Pallet Dimension"/>
<field name="height"/>
<field name="width"/>
<field name="length"/>
</group>
<separator colspan="4" string="Description"/>
<field name="name"/>
</form>
</field>
<separator string="Description for Quotations"/>
<field name="description_sale" placeholder="note to be displayed on quotations..."/>
</page>
</notebook>
</sheet>
<div class="oe_chatter">
<field name="message_follower_ids" widget="mail_followers"/>
<field name="message_ids" widget="mail_thread"/>
</div>
</form>

Answer 1

It's not forbidden to modify the standard modules, but it is generally recommended to write your own modules to extend OpenERP.
I don't know how much experience you've got with OpenERP (if you are new to OpenERP, the problem could be caused by very simple mistakes), so forgive me for assuming you are a newbie.
Have you restarted OpenERP and reinstalled the product module?
Is the cal_change_event() method defined in a class whose _name = "product.product" ?
Could you post your XML code? The problem could be nothing to do with your Python code.

Answer 2

All the code here works FINE. The problem seemed to be my CENTOS install.
This code works correctly on WINDOWS and a new XUBUNTU Machine I just made.
Unfortunately the reason why it didn't work in CentOS still eludes me.
I'm closing this topic, hopefully the code pf my .XML and .PY can be a useful template for all those who wish to have personalized fields in their products and have them interactively change. thanks Wenshan for your assistance, as you noticed in the beginning, nothing was wrong with the code.