code: def array_keys(self):
          
          for key in sorted(listdir(self._store, self._path)):
              path = self._key_prefix + key
              if contains_array(self._store, path):
                  yield key
docs: Return an iterator over member names for arrays only.
  
          Examples
          --------
          >>> import zarr
          >>> g1 = zarr.group()
          >>> g2 = g1.create_group('foo')
          >>> g3 = g1.create_group('bar')
          >>> d1 = g1.create_dataset('baz', shape=100, chunks=10)
          >>> d2 = g1.create_dataset('quux', shape=200, chunks=20)
          >>> sorted(g1.array_keys())
          ['baz', 'quux']