title: How to change the default value of a property field in Odoo (old API)?
body: <p>I'm trying to change the default value of some property fields such as: 'cost_method', 'product_type' and 'valuation' of the 'product' module but I can only change the non-property fields only.</p>
  
  <p>What I tried:
  - I created a new module and inherited the 'product.template' model and overridden the '_default' dictionary only but it didn't work.</p>
  
  <ul>
  <li>I created new fields with the same name but of another type (selection) not property but neither did this work.</li>
  </ul>
  
  <p>The code:  </p>
  
  <pre><code> _name = "product.template"
   _inherit = "product.template"
  </code></pre>
  
  <p>_columns = {</p>
  
  <p>'cost_method': fields.selection([('average', 'Average Price'),('standard', 'Standard Price'),  ('real', 'Real Price')])
          ,'type': fields.selection([('product', 'Stockable Product'),('consu', 'Consumable'),('service','Service')], 'Product Type', required=True, help="Consumable are product where you don't manage stock, a service is a non-material product provided by a company or an individual.")
   ,'company_id': fields.many2one('res.company', 'Company', required=False)
          }</p>
  
  <pre><code> _defaults = {
      'company_id': False
      ,'type' : 'product'
      , 'cost_method': 'average'
      , 'barcode':'555'
  }
  </code></pre>