code: def _interpolate(start, end, step, total_steps):
          
          diff = end - start
          progress = step / (total_steps - 1)
          return start + progress * diff
docs: Interpolate a value from start to end at a given progress.
  
          :param start: The start value.
          :param end: The end value.
          :param step: The current step.
          :param total_steps: The total number of steps.
          :return: The interpolated value at the given progress.