class_docstr: An FXRateReader backed by HDF5.
  
  Parameters
  ----------
  group : h5py.Group
      Top-level group written by an :class:`HDF5FXRateWriter`.
  default_rate : str
      Rate to use when ``get_rates`` is called requesting the default rate.
code: def version(self):
      try:
          return self._group.attrs["version"]
      except KeyError:
          # TODO: Remove this.
          return 0
  
imports: from interface import implements
  import h5py
  from logbook import Logger
  import numpy
  import pandas
  from zipline.utils.memoize import lazyval
  from zipline.utils.numpy_utils import bytes_array_to_native_str_object_array
  from .base import FXRateReader, DEFAULT_FX_RATE
  from .utils import check_dts, is_sorted_ascending
label_desc: Use image node_id 3 for calling the HDF5FXRateReader obj's underlying member method code with example usage: obj.version() and returns: self, int