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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fill_taxid2asscs(taxid2asscs_usr, taxid2asscs_ret):
 """Fill user taxid2asscs for backward compatibility."""

        for taxid, ab_ret in taxid2asscs_ret.items():
            taxid2asscs_usr[taxid]['ID2GOs'] = ab_ret['ID2GOs']
            taxid2asscs_usr[taxid]['GO2IDs'] = ab_ret['GO2IDs']