Download Ontologies, if necessary.

def download_go_basic_obo(obo="go-basic.obo", prt=sys.stdout, loading_bar=True):
    """Download Ontologies, if necessary."""
    if not os.path.isfile(obo):
        http = "http://purl.obolibrary.org/obo/go"
        if "slim" in obo:
            http = "http://www.geneontology.org/ontology/subsets"
            # http = 'http://current.geneontology.org/ontology/subsets'
        obo_remote = "{HTTP}/{OBO}".format(HTTP=http, OBO=os.path.basename(obo))
        dnld_file(obo_remote, obo, prt, loading_bar)
    else:
        if prt is not None:
            prt.write("  EXISTS: {FILE}\n".format(FILE=obo))
    return obo