code: def sparsify(dirname, output_every):
      
      fnames = get_filenames(dirname)
      output_every_old = get_output_every(dirname)
      if output_every % output_every_old != 0:
          raise ValueError('Directory with output_every={} cannot be coerced to'
                           'desired new value.'.format(output_every_old))
      keep_every = output_every // output_every_old
      fnames_to_keep = fnames[::keep_every]
      fnames_to_delete = set(fnames) - set(fnames_to_keep)
      for fname in fnames_to_delete:
          os.remove(fname)
docs: Remove files from an output directory at regular interval, so as to
      make it as if there had been more iterations between outputs. Can be used
      to reduce the storage size of a directory.
  
      If the new number of iterations between outputs is not an integer multiple
      of the old number, then raise an exception.
  
      Parameters
      ----------
      dirname: str
          A path to a directory.
      output_every: int
          Desired new number of iterations between outputs.
  
      Raises
      ------
      ValueError
          The directory cannot be coerced into representing `output_every`.