>>> dir(a)
['__class__',
 '__delattr__',
 '__dict__',
 '__doc__',
 '__enter__',
 '__exit__',
 '__format__',
 '__getattribute__',
 '__hash__',
 '__init__',
 '__module__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '__weakref__',
 '_add_vector',
 '_add_vector_reader',
 '_add_wordsets',
 '_added',
 '_check_state',
 '_close_all',
 '_doc_boost',
 '_doc_offsets',
 '_document_segment',
 '_field_boost',
 '_getsegment',
 '_segment_and_docnum',
 '_unique_cache',
 '_unique_fields',
 'add_document',
 'add_field',
 'add_reader',
 'add_spell_words',
 'blocklimit',
 'cancel',
 'commit',
 'dawg',
 'delete_by_query',
 'delete_by_term',
 'delete_document',
 'deleted_count',
 'docnum',
 'fieldlength_totals',
 'generation',
 'has_deletions',
 'indexname',
 'is_closed',
 'is_deleted',
 'lengthfile',
 'name',
 'pool',
 'reader',
 'remove_field',
 'schema',
 'searcher',
 'segment_number',
 'segments',
 'storage',
 'storedfields',
 'termswriter',
 'update_document',
 'vectorindex',
 'vpostwriter',
 'wordsets',
 'writelock']