Thanks all  

am going for the customization   

the thing is i don't want the sequencing or auto generating  product default code 

only on the  variant creation default product code to be inherited product Default code form the template.Product_Default_code to product.product_default_code || variant  

what am saying anyone can help me coding this  

Just for clarification :-

Product Name : Air Filter,   internal reference: 1901010, Variant: Type D & E

automatically the variant creation would be 

internal Reference    Product Name

1901010-D                      Air Filter 

1901010-E                       Air Filter

thanks.

You could try the following approach.

1. Make Internal Reference required on the Product Template​

2. Define a sequence (with no gaps) and use it to assign the sequence number to Internal Reference using an Automated Action

3. Define an Automated Action on Product Variant to set the Internal Reference value based on the criteria you need. 

Hi,

There is a lot of modules available in the Odoo app store for the product code generation, but it does not match with what exactly you are looking for. For your requirement I think, you have to customize the system accordingly as per the need.

Anyway have a look at this module: Product Code

Thanks