env_wrappers.py

import gym
import numpy as np


class PendulumActionNormalizer(gym.ActionWrapper):
    """Rescale and relocate the actions."""

    def action(self, action: np.ndarray) -> np.ndarray:
        """Change the range (-1, 1) to (low, high)."""
        low = self.action_space.low
        high = self.action_space.high

        scale_factor = (high - low) / 2
        reloc_factor = high - scale_factor

        action = action * scale_factor + reloc_factor
        action = np.clip(action, low, high)

        return action

    def reverse_action(self, action: np.ndarray) -> np.ndarray:
        """Change the range (low, high) to (-1, 1)."""
        low = self.action_space.low
        high = self.action_space.high

        scale_factor = (high - low) / 2
        reloc_factor = high - scale_factor

        action = (action - reloc_factor) / scale_factor
        action = np.clip(action, -1.0, 1.0)

        return action