Download associations from NCBI, if necessary

def download_ncbi_associations(gene2go="gene2go", prt=sys.stdout, loading_bar=True):
    """Download associations from NCBI, if necessary"""
    # Download: ftp://ftp.ncbi.nlm.nih.gov/gene/DATA/gene2go.gz
    gzip_file = "{GENE2GO}.gz".format(GENE2GO=gene2go)
    if not os.path.isfile(gene2go):
        file_remote = "ftp://ftp.ncbi.nlm.nih.gov/gene/DATA/{GZ}".format(
            GZ=os.path.basename(gzip_file))
        dnld_file(file_remote, gene2go, prt, loading_bar)
    else:
        if prt is not None:
            prt.write("  EXISTS: {FILE}\n".format(FILE=gene2go))
    return gene2go