Generates a file from a template, interpolating config values.

def GenerateFile(self, input_filename=None, output_filename=None):
    """Generates a file from a template, interpolating config values."""
    if input_filename is None:
      input_filename = output_filename + ".in"
    if output_filename[-3:] == ".in":
      output_filename = output_filename[:-3]
    logging.debug("Generating file %s from %s", output_filename, input_filename)

    with io.open(input_filename, "r") as fd:
      data = fd.read()

    with io.open(output_filename, "w") as fd:
      fd.write(config.CONFIG.InterpolateValue(data, context=self.context))