How to check what are attributes available in one object?

opn = open('file1.txt')

dir(opn)

Output:

['_CHUNK_SIZE',
 '__class__',
 '__del__',
 '__delattr__',
 '__dict__',
 '__dir__',
 '__doc__',
 '__enter__',
 '__eq__',
 '__exit__',
 '__format__',
 '__ge__',
 '__getattribute__',
 '__getstate__',
 '__gt__',
 '__hash__',
 '__init__',
 '__init_subclass__',
 '__iter__',
 '__le__',
 '__lt__',
 '__ne__',
 '__new__',
 '__next__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '_checkClosed',
 '_checkReadable',
 '_checkSeekable',
 '_checkWritable',
 '_finalizing',
 'buffer',
 'close',
 'closed',
 'detach',
 'encoding',
 'errors',
 'fileno',
 'flush',
 'isatty',
 'line_buffering',
 'mode',
 'name',
 'newlines',
 'read',
 'readable',
 'readline',
 'readlines',
 'seek',
 'seekable',
 'tell',
 'truncate',
 'writable',
 'write',
 'writelines']