How to use the t5.data.postprocessors.qa function in t5

"squad_v010_allanswers",
    TfdsTask,
    tfds_name="squad/plain_text:0.1.0",
    text_preprocessor=preprocessors.squad,
    postprocess_fn=postprocessors.qa,
    metric_fns=[metrics.qa],
    sentencepiece_model_path=DEFAULT_SPM_PATH)

# Maximized evaluation metrics over all answers.
TaskRegistry.add(
    "squad_v010_context_free",
    TfdsTask,
    tfds_name="squad/plain_text:0.1.0",
    text_preprocessor=functools.partial(
        preprocessors.squad, include_context=False),
    postprocess_fn=postprocessors.qa,
    metric_fns=[metrics.qa],
    sentencepiece_model_path=DEFAULT_SPM_PATH)

# Squad span prediction task instead of text.
TaskRegistry.add(
    "squad_v010_allanswers_span",
    TfdsTask,
    tfds_name="squad/plain_text:0.1.0",
    text_preprocessor=preprocessors.squad_span_space_tokenized,
    postprocess_fn=postprocessors.span_qa,
    metric_fns=[metrics.span_qa],
    sentencepiece_model_path=DEFAULT_SPM_PATH)

# Deprecated: Use `squad_v010_allanswers` instead.
TaskRegistry.add(
    "squad_v010",

def _get_glue_postprocess_fn(builder_config):
  if builder_config.name == "stsb":
    return postprocessors.string_to_float
  elif builder_config.name == "multirc":
    return postprocessors.multirc
  elif builder_config.name == "record":
    return postprocessors.qa
  else:
    return functools.partial(
        postprocessors.string_label_to_class_id,
        label_classes=builder_config.label_classes,
    )