text: import tarfile
  
  print('creating archive')
  with tarfile.open('tarfile_append.tar', mode='w') as out:
      out.add('README.txt')
  
  print('contents:',)
  with tarfile.open('tarfile_append.tar', mode='r') as t:
      print([m.name for m in t.getmembers()])
  
  print('adding index.rst')
  with tarfile.open('tarfile_append.tar', mode='a') as out:
      out.add('index.rst')
  
  print('contents:',)
  with tarfile.open('tarfile_append.tar', mode='r') as t:
      print([m.name for m in t.getmembers()])
  