def create_constant_learning_rate_fn(base_learning_rate):
  """Create a constant learning rate function.

  Args:
    base_learning_rate: learning rate that will always be returned

  Returns:
    function of the form f(step) -> learning_rate
  """
  def step_fn(step):  ## pylint: disable=unused-argument
    return base_learning_rate
  return step_fn