Stable-Baselines 3 部分源代码解读 ./ppo/ppo.py

前言

阅读PPO相关的源码，了解一下标准库是如何建立PPO算法以及各种tricks的，以便于自己的复现。

在Pycharm里面一直跳转，可以看到PPO类是最终继承于基类，也就是这个py文件的内容。

所以阅读源码就先从这里开始。: )

import 包

import warnings
from typing import Any, Dict, Optional, Type, TypeVar, Unionimport numpy as np
import torch as th
from gym import spaces
from torch.nn import functional as Ffrom stable_baselines3.common.on_policy_algorithm import OnPolicyAlgorithm
from stable_baselines3.common.policies import ActorCriticCnnPolicy, ActorCriticPolicy, BasePolicy, MultiInputActorCriticPolicy
from stable_baselines3.common.type_aliases import GymEnv, MaybeCallback, Schedule
from stable_baselines3.common.utils import explained_variance, get_schedule_fn

PPO 类

这是面向使用者的浅层的PPO，也就是能直接调用的类

作者在源码中给出了PPO的论文、引用了谁的源代码编写的以及一个引进PPO的讲解。

policy、env和learning_rate三者与基类base-class.py的一致

n_steps表示每次更新前需要经过的时间步，作者在这里给出了n_steps * n_envs的例子，可能的意思是，如果环境是重复的多个，打算做并行训练的话，那么就是每个子环境的时间步乘以环境的数量

batch_size经验回放的最小批次信息

gamma、gae_lambda、clip_range、clip_range_vf均是具有默认值的参数，分别代表“折扣因子”、“GAE奖励中平衡偏置和方差的参数”、“为网络参数而限制幅度的范围”、“为值函数网络参数而限制幅度的范围”

normalize_advantage标志是否需要归一化优势（advantage）

ent_coef、vf_coef损失计算的熵系数

max_grad_norm最大的梯度长度，梯度下降的限幅

use_sde、sde_sample_freq是状态独立性探索，只适用于连续环境，与基类base-class.py的一致

target_kl限制每次更新时KL散度不能太大，因为clipping限幅不能防止大量更新

剩下的参数与基类base-class.py的一致

class PPO(OnPolicyAlgorithm):"""Proximal Policy Optimization algorithm (PPO) (clip version)Paper: https://arxiv.org/abs/1707.06347Code: This implementation borrows code from OpenAI Spinning Up (https://github.com/openai/spinningup/)https://github.com/ikostrikov/pytorch-a2c-ppo-acktr-gail andStable Baselines (PPO2 from https://github.com/hill-a/stable-baselines)Introduction to PPO: https://spinningup.openai.com/en/latest/algorithms/ppo.html:param policy: The policy model to use (MlpPolicy, CnnPolicy, ...):param env: The environment to learn from (if registered in Gym, can be str):param learning_rate: The learning rate, it can be a functionof the current progress remaining (from 1 to 0):param n_steps: The number of steps to run for each environment per update(i.e. rollout buffer size is n_steps * n_envs where n_envs is number of environment copies running in parallel)NOTE: n_steps * n_envs must be greater than 1 (because of the advantage normalization)See https://github.com/pytorch/pytorch/issues/29372:param batch_size: Minibatch size:param n_epochs: Number of epoch when optimizing the surrogate loss:param gamma: Discount factor:param gae_lambda: Factor for trade-off of bias vs variance for Generalized Advantage Estimator:param clip_range: Clipping parameter, it can be a function of the current progressremaining (from 1 to 0).:param clip_range_vf: Clipping parameter for the value function,it can be a function of the current progress remaining (from 1 to 0).This is a parameter specific to the OpenAI implementation. If None is passed (default),no clipping will be done on the value function.IMPORTANT: this clipping depends on the reward scaling.:param normalize_advantage: Whether to normalize or not the advantage:param ent_coef: Entropy coefficient for the loss calculation:param vf_coef: Value function coefficient for the loss calculation:param max_grad_norm: The maximum value for the gradient clipping:param use_sde: Whether to use generalized State Dependent Exploration (gSDE)instead of action noise exploration (default: False):param sde_sample_freq: Sample a new noise matrix every n steps when using gSDEDefault: -1 (only sample at the beginning of the rollout):param target_kl: Limit the KL divergence between updates,because the clipping is not enough to prevent large updatesee issue #213 (cf https://github.com/hill-a/stable-baselines/issues/213)By default, there is no limit on the kl div.:param tensorboard_log: the log location for tensorboard (if None, no logging):param policy_kwargs: additional arguments to be passed to the policy on creation:param verbose: Verbosity level: 0 for no output, 1 for info messages (such as device or wrappers used), 2 fordebug messages:param seed: Seed for the pseudo random generators:param device: Device (cpu, cuda, ...) on which the code should be run.Setting it to auto, the code will be run on the GPU if possible.:param _init_setup_model: Whether or not to build the network at the creation of the instance"""# PPO策略中限制的可以用字符串的策略就是下面三个# 连续环境使用时一般会提示选择"MultiInputPolicy"policy_aliases: Dict[str, Type[BasePolicy]] = {"MlpPolicy": ActorCriticPolicy,"CnnPolicy": ActorCriticCnnPolicy,"MultiInputPolicy": MultiInputActorCriticPolicy,}# 输入的一些默认参数表列可以为调参提供参考def __init__(self,policy: Union[str, Type[ActorCriticPolicy]],env: Union[GymEnv, str],learning_rate: Union[float, Schedule] = 3e-4,n_steps: int = 2048,batch_size: int = 64,n_epochs: int = 10,gamma: float = 0.99,gae_lambda: float = 0.95,clip_range: Union[float, Schedule] = 0.2,clip_range_vf: Union[None, float, Schedule] = None,normalize_advantage: bool = True,ent_coef: float = 0.0,vf_coef: float = 0.5,max_grad_norm: float = 0.5,use_sde: bool = False,sde_sample_freq: int = -1,target_kl: Optional[float] = None,tensorboard_log: Optional[str] = None,policy_kwargs: Optional[Dict[str, Any]] = None,verbose: int = 0,seed: Optional[int] = None,device: Union[th.device, str] = "auto",_init_setup_model: bool = True,):super().__init__(policy,env,learning_rate=learning_rate,n_steps=n_steps,gamma=gamma,gae_lambda=gae_lambda,ent_coef=ent_coef,vf_coef=vf_coef,max_grad_norm=max_grad_norm,use_sde=use_sde,sde_sample_freq=sde_sample_freq,tensorboard_log=tensorboard_log,policy_kwargs=policy_kwargs,verbose=verbose,device=device,seed=seed,_init_setup_model=False,supported_action_spaces=(spaces.Box,spaces.Discrete,spaces.MultiDiscrete,spaces.MultiBinary,),)# 合理性、完整性检查，如果需要normalize的话，需要保证batch_size参数大于1# Sanity check, otherwise it will lead to noisy gradient and NaN# because of the advantage normalizationif normalize_advantage:assert (batch_size > 1), "`batch_size` must be greater than 1. See https://github.com/DLR-RM/stable-baselines3/issues/440"if self.env is not None:# Check that `n_steps * n_envs > 1` to avoid NaN# when doing advantage normalizationbuffer_size = self.env.num_envs * self.n_steps# 如果buffer_size等于1但是又需要normalize_advantage标志时# 报错，输出当前的需要运行的时间步和当前的环境数量assert buffer_size > 1 or (not normalize_advantage), f"`n_steps * n_envs` must be greater than 1. Currently n_steps={self.n_steps} and n_envs={self.env.num_envs}"# rollouts的池子大小必须与最小池子数量mini-batch一致，也就是能整除# 这样才能一份一份的导入（我的理解是这样）# Check that the rollout buffer size is a multiple of the mini-batch sizeuntruncated_batches = buffer_size // batch_size# 不是整除的话，就爆出警告if buffer_size % batch_size > 0:warnings.warn(f"You have specified a mini-batch size of {batch_size},"f" but because the `RolloutBuffer` is of size `n_steps * n_envs = {buffer_size}`,"f" after every {untruncated_batches} untruncated mini-batches,"f" there will be a truncated mini-batch of size {buffer_size % batch_size}\n"f"We recommend using a `batch_size` that is a factor of `n_steps * n_envs`.\n"f"Info: (n_steps={self.n_steps} and n_envs={self.env.num_envs})")self.batch_size = batch_sizeself.n_epochs = n_epochsself.clip_range = clip_rangeself.clip_range_vf = clip_range_vfself.normalize_advantage = normalize_advantageself.target_kl = target_klif _init_setup_model:self._setup_model()def _setup_model(self) -> None:super()._setup_model()# Transform (if needed) learning rate and clip range (for PPO) to callable.# 将输入的限制幅度转变成可以调用的变量# Initialize schedules for policy/value clippingself.clip_range = get_schedule_fn(self.clip_range)# 对self.clip_range_vf参数做数据类型和正值检查if self.clip_range_vf is not None:if isinstance(self.clip_range_vf, (float, int)):assert self.clip_range_vf > 0, "`clip_range_vf` must be positive, " "pass `None` to deactivate vf clipping"self.clip_range_vf = get_schedule_fn(self.clip_range_vf)def train(self) -> None:"""Update policy using the currently gathered rollout buffer."""# 将模型设置成训练模式，这会影响到batch norm和正则化# Switch to train mode (this affects batch norm / dropout)self.policy.set_training_mode(True)# 更新学习率，如果学习率是与当前进度有关的数值# Update optimizer learning rateself._update_learning_rate(self.policy.optimizer)# 计算限幅参数，输入的是与当前进度有关的学习率，动态变化包括clip_range和clip_range_vf# 也就是策略网络和价值网络# Compute current clip rangeclip_range = self.clip_range(self._current_progress_remaining)# Optional: clip range for the value functionif self.clip_range_vf is not None:clip_range_vf = self.clip_range_vf(self._current_progress_remaining)# 初始化各种损失的记录# 熵损失、策略梯度损失、价值损失和限制参数entropy_losses = []pg_losses, value_losses = [], []clip_fractions = []# 设置continue_training为True，表示现在处于持续性训练状态continue_training = True# train for n_epochs epochs# self.n_epochs是训练次数for epoch in range(self.n_epochs):# 记录近似的KL散度数值approx_kl_divs = []# Do a complete pass on the rollout buffer# 将rollout_buffer池子用batch_size做分割，遍历每一个循环for rollout_data in self.rollout_buffer.get(self.batch_size):# 取出每一小批的动作数据actions = rollout_data.actions# 如果是离散动作空间的话，专程浮点型数据并拉直if isinstance(self.action_space, spaces.Discrete):# Convert discrete action from float to longactions = rollout_data.actions.long().flatten()# 判断是否使用了状态独立性探索，如果使用了状态独立性探索# 那么就重置噪声# Re-sample the noise matrix because the log_std has changedif self.use_sde:self.policy.reset_noise(self.batch_size)# 根据策略、观测的数据和动作，输出价值、对数概率以及熵values, log_prob, entropy = self.policy.evaluate_actions(rollout_data.observations, actions)# 再把价值再做拉直values = values.flatten()# 对经验池子的advantages做Normalize# Normalize的公式是advantages里面的数值减去advantages的均值# 然后再除以advantages的均值的方差（自己复现的话，也可以调用其他库的方法）# Normalize advantageadvantages = rollout_data.advantages# Normalization does not make sense if mini batchsize == 1, see GH issue #325if self.normalize_advantage and len(advantages) > 1:advantages = (advantages - advantages.mean()) / (advantages.std() + 1e-8)# 输出先后动作概率的差异值# ratio between old and new policy, should be one at the first iterationratio = th.exp(log_prob - rollout_data.old_log_prob)# 策略的损失是优势数值乘以比率，以及限制幅度的优势之间的负最小值# 就是论文的公式# clipped surrogate losspolicy_loss_1 = advantages * ratiopolicy_loss_2 = advantages * th.clamp(ratio, 1 - clip_range, 1 + clip_range)policy_loss = -th.min(policy_loss_1, policy_loss_2).mean()# 记录在刚才初始化的日志记录器里面# Loggingpg_losses.append(policy_loss.item())clip_fraction = th.mean((th.abs(ratio - 1) > clip_range).float()).item()clip_fractions.append(clip_fraction)# 如果价值没有限幅的话，就直接输出# 有限制幅度的话，那么就是限幅增量th.clamp()+原来的数值if self.clip_range_vf is None:# No clippingvalues_pred = valueselse:# Clip the difference between old and new value# NOTE: this depends on the reward scalingvalues_pred = rollout_data.old_values + th.clamp(values - rollout_data.old_values, -clip_range_vf, clip_range_vf)# 构建损失函数并记录下来# Value loss using the TD(gae_lambda) targetvalue_loss = F.mse_loss(rollout_data.returns, values_pred)value_losses.append(value_loss.item())# 如果没有熵损失，那么就直接取得均值的副对数概率，如果有熵损失那么就是熵损失的均值# Entropy loss favor explorationif entropy is None:# Approximate entropy when no analytical formentropy_loss = -th.mean(-log_prob)else:entropy_loss = -th.mean(entropy)entropy_losses.append(entropy_loss.item())# 最终的损失就是策略损失和加了系数的熵损失和价值函数损失loss = policy_loss + self.ent_coef * entropy_loss + self.vf_coef * value_loss# Calculate approximate form of reverse KL Divergence for early stopping# see issue #417: https://github.com/DLR-RM/stable-baselines3/issues/417# and discussion in PR #419: https://github.com/DLR-RM/stable-baselines3/pull/419# and Schulman blog: http://joschu.net/blog/kl-approx.html# 计算近似KL散度并记录在列表中with th.no_grad():log_ratio = log_prob - rollout_data.old_log_probapprox_kl_div = th.mean((th.exp(log_ratio) - 1) - log_ratio).cpu().numpy()approx_kl_divs.append(approx_kl_div)# 如果target_kl存在且近似KL散度太大了，也就是更新程度太大，就提前结束，并报错if self.target_kl is not None and approx_kl_div > 1.5 * self.target_kl:continue_training = Falseif self.verbose >= 1:print(f"Early stopping at step {epoch} due to reaching max kl: {approx_kl_div:.2f}")break# 对损失做优化# Optimization stepself.policy.optimizer.zero_grad()loss.backward()# 限制幅度避免较大的更新# Clip grad normth.nn.utils.clip_grad_norm_(self.policy.parameters(), self.max_grad_norm)self.policy.optimizer.step()self._n_updates += 1if not continue_training:breakexplained_var = explained_variance(self.rollout_buffer.values.flatten(), self.rollout_buffer.returns.flatten())# Logsself.logger.record("train/entropy_loss", np.mean(entropy_losses))self.logger.record("train/policy_gradient_loss", np.mean(pg_losses))self.logger.record("train/value_loss", np.mean(value_losses))self.logger.record("train/approx_kl", np.mean(approx_kl_divs))self.logger.record("train/clip_fraction", np.mean(clip_fractions))self.logger.record("train/loss", loss.item())self.logger.record("train/explained_variance", explained_var)if hasattr(self.policy, "log_std"):self.logger.record("train/std", th.exp(self.policy.log_std).mean().item())self.logger.record("train/n_updates", self._n_updates, exclude="tensorboard")self.logger.record("train/clip_range", clip_range)if self.clip_range_vf is not None:self.logger.record("train/clip_range_vf", clip_range_vf)def learn(self: SelfPPO,total_timesteps: int,callback: MaybeCallback = None,log_interval: int = 1,tb_log_name: str = "PPO",reset_num_timesteps: bool = True,progress_bar: bool = False,) -> SelfPPO:# 这个函数主要是给用户做调用，在初始化PPO类之后，将这些参数引进来就可以# total_timesteps总的需要的时间步return super().learn(total_timesteps=total_timesteps,callback=callback,log_interval=log_interval,tb_log_name=tb_log_name,reset_num_timesteps=reset_num_timesteps,progress_bar=progress_bar,)