I have performed an entrapment experiment with X!Tandem. All target labels start with ">generic|T_" and all decoy labels start with ">generic|D_". Using Pyteomics I have read them with tandem.TandemXML(result.t.xml) and now I need to filter them using an FDR threshold. Therefore, I use tandem.filter(result.t.xml, fdr=0.05, is_decoy = "D_"), but it throws a KeyError: KeyError: 'D_'.
How can I solve this?
Thanks in advance!