let's start with this ...

gistfile1.py

if evidence:
            for evidence_var in evidence:
                for factor in working_factors[evidence_var]:
                    factor_reduced = factor.reduce('{evidence_var}_{state}'.format(evidence_var=evidence_var,
                                                                                   state=evidence[evidence_var]),
                                                   inplace=False)
                    for var in factor_reduced.scope():
                        working_factors[var].remove(factor)
                        working_factors[var].add(factor_reduced)
                del working_factors[evidence_var]