class_docstr: PyTorch Lightning implementation of PPO.
  
  Example:
      model = PPOLightning("CartPole-v0")
  Train:
      trainer = Trainer()
      trainer.fit(model)
code: def critic_loss(
      self, state, action, logp_old, qval, adv
  ) -> torch.Tensor:
      value = self.critic(state)
      return (qval - value).pow(2).mean()
  
imports: import argparse
  from typing import Callable, Iterator, List, Tuple
  import gym
  import torch
  from lightning.pytorch import LightningModule, Trainer, cli_lightning_logo, seed_everything
  from torch import nn
  from torch.distributions import Categorical, Normal
  from torch.optim.optimizer import Optimizer
  from torch.utils.data import DataLoader, IterableDataset
label_desc: Use image node_id 7 for calling the PPOLightning obj's underlying member method code with example usage: obj.critic_loss(state, action, logp_old, qval, adv) and returns: unknown