code: def default_hub(hub_name, genome, email, short_label=None, long_label=None):
      
      if short_label is None:
          short_label = hub_name
      if long_label is None:
          long_label = short_label
  
      hub = Hub(
          hub=hub_name,
          short_label=short_label,
          long_label=long_label,
          email=email)
  
      genome = Genome(genome)
      genomes_file = GenomesFile()
      trackdb = TrackDb()
      hub.add_genomes_file(genomes_file)
      genomes_file.add_genome(genome)
      genome.add_trackdb(trackdb)
      return hub, genomes_file, genome, trackdb
docs: Returns a fully-connected set of hub components using default filenames.
  
      Parameters
      ----------
  
      hub_name : str
          Name of the hub
  
      genome : str
          Assembly name (hg38, dm6, etc)
  
      email : str
          Email to include with hub.
  
      short_label : str
          Short label for the hub. If None, defaults to the value of `hub_name`
  
      long_label : str
          Long label for the hub. If None, defaults to the value of `short_label`.