<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def david_go(refseq_list, annot=('SP_PIR_KEYWORDS', 'GOTERM_BP_FAT', 'GOTERM_CC_FAT', 'GOTERM_MF_FAT')):
 """ open a web-browser to the DAVID online enrichment tool Parameters refseq_list : list list of refseq names to check for enrichment annot : list iterable of DAVID annotations to check for enrichment """

        URL = "http://david.abcc.ncifcrf.gov/api.jsp?type=REFSEQ_MRNA&ids=%s&tool=term2term&annot="
        import webbrowser
        webbrowser.open(URL % ",".join(set(refseq_list)) + ",".join(annot))