You can find the code in "Procurement" addon's "procurement.py" file.

class product_template(osv.osv):
    _inherit="product.template"

    _columns = {
        'type': fields.selection([('product','Stockable Product'),('consu', 'Consumable'),('service','Service')], 'Product Type', required=True, help="Consumable: Will not imply stock management for this product. \nStockable product: Will imply stock management for this product."),
        'procure_method': fields.selection([('make_to_stock','Make to Stock'),('make_to_order','Make to Order')], 'Procurement Method', required=True, help="Make to Stock: When needed, the product is taken from the stock or we wait for replenishment. \nMake to Order: When needed, the product is purchased or produced."),
        'supply_method': fields.selection([('produce','Manufacture'),('buy','Buy')], 'Supply Method', required=True, help="Manufacture: When procuring the product, a manufacturing order or a task will be generated, depending on the product type. \nBuy: When procuring the product, a purchase order will be generated."),
    }
    _defaults = {
        'procure_method': 'make_to_stock',
        'supply_method': 'buy',
    }