code: def vcf_to_df(canvasvcfs, exonbed, cpus):
      
      df = pd.DataFrame()
      p = Pool(processes=cpus)
      results = []
      args = [(x, exonbed, i) for (i, x) in enumerate(canvasvcfs)]
      r = p.map_async(vcf_to_df_worker, args,
                      callback=results.append)
      r.wait()
  
      for res in results:
          df = df.append(res, ignore_index=True)
      return df
docs: Compile a number of vcf files into tsv file for easy manipulation