Obtaining a mapping of RefSeq ACs to Uniprot ACs
You have a bunch of options:


You can use Biomart.
Biomart is a standalone tool, but also have a pyton and R libraries. So it gives you more options depending on your preferred programming language. This is a widely used tool and in general works well.


biomart http://www.biomart.org/
biomart python library
biomart R library (from bioconductor)
Biomart is widely used and have extensive documentation.

Use a python library called pyEntrezID 
https://pypi.python.org/pypi/pyEntrezId/1.4.7
You can do all sort of conversions of ids, however I've never tried it.
You can try NCBI eutils or one of the Ensembl REST API endpoints