code: def _read_truth_freqs(in_file):
      
      out = {}
      with VariantFile(in_file) as bcf_in:
          for rec in bcf_in:
              freq = float(rec.info.get("VAF", 1.0))
              out[_get_key(rec)] = freq
      return out
docs: Read frequency of calls from truth VCF.
  
      Currently handles DREAM data, needs generalization for other datasets.