code: def make_gffutils_db(gtf, db):
      
      import gffutils
      out_db = gffutils.create_db(gtf,
                                  db,
                                  keep_order=True,
                                  infer_gene_extent=False)
      return out_db
docs: Make database for gffutils. 
  
      Parameters
      ----------
      gtf : str
          Path to Gencode gtf file.
  
      db : str
          Path to save database to. 
  
      Returns
      -------
      out_db : gffutils.FeatureDB
          gffutils feature database.