How do I import attributes with the feed mapper? I have a Drupal 7 instance with Ubercart 3, and I'm also using the Ubercart Feed Mappers module to map out the importing of product fields. I have all the fields, images and categories working well, but not attributes.

I've searched high and low for an answer or a short how to for importing attributes and multiple attributes for each product but with no success. How can I achieve it?
You need 'UC Feeds Product Importer' a sub module built to import all the product related fields.

check this: https://drupal.org/node/1802908


Create an importer (at admin/structure/feeds/create). Or try my default importer module, which creates a csv importer from all Ubercart fields - including attributes - automatically. If you use it, please leave feedback on the issue!
Download the template from the import page (if you use the default importer above, it will be at /import/uc_feeds_product_importer/template)
Fill in the template. For each attribute option you want enabled, fill in at least one of the cells for weight, price, or cost (a zero value works). If you fill in at least one of the three, any unfilled will default to zero. If you leave all three blank, that option will not be enabled on the imported product.
Import the completed csv at /import/uc_feeds_product_importer (if you're using my module above), otherwise go to /import and choose the importer you created.