/ Machine Learning

A flexible and superfast PyTorch deep Reinforcement Learning platform

A flexible and superfast PyTorch deep Reinforcement Learning platform


Tianshou (天授) is a reinforcement learning platform based on pure PyTorch. Unlike existing reinforcement learning libraries, which are mainly based on TensorFlow, have many nested classes, unfriendly API, or slow-speed, Tianshou provides a fast-speed framework and pythonic API for building the deep reinforcement learning agent. The supported interface algorithms include:

  • Policy Gradient (PG)
  • Deep Q-Network (DQN)
  • Double DQN (DDQN) with n-step returns
  • Advantage Actor-Critic (A2C)
  • Deep Deterministic Policy Gradient (DDPG)
  • Proximal Policy Optimization (PPO)
  • Twin Delayed DDPG (TD3)
  • Soft Actor-Critic (SAC)

Tianshou supports parallel workers for all algorithms as well. All of these algorithms are reformatted as replay-buffer based algorithms.

Tianshou is still under development. More algorithms are going to be added and we always welcome contributions to help make Tianshou better. If you would like to contribute, please check out CONTRIBUTING.md.


Tianshou is currently hosted on PyPI. You can simply install Tianshou with the following command:

pip3 install tianshou

You can also install with the newest version through GitHub:

pip3 install git+https://github.com/thu-ml/[email protected]

After installation, open your python console and type

import tianshou as ts

If no error occurs, you have successfully installed Tianshou.


The tutorials and API documentation are hosted on https://tianshou.readthedocs.io.

The example scripts are under test/ folder and examples/ folder.

Why Tianshou?


Tianshou is a lightweight but high-speed reinforcement learning platform. For example, here is a test on a laptop (i7-8750H + GTX1060). It only uses 3 seconds for training a agent based on vanilla policy gradient on the CartPole-v0 task.


We select some of famous (>1k stars) reinforcement learning platforms. Here is the benchmark result for other algorithms and platforms on toy scenarios: (tested on the same laptop as mentioned above)

RL Platform Tianshou Baselines Ray/RLlib PyTorch DRL rlpyt
GitHub Stars GitHub stars GitHub stars GitHub stars GitHub stars GitHub stars
Algo - Task PyTorch TensorFlow TF/PyTorch PyTorch PyTorch
PG - CartPole 9.03±4.18s None 15.77±6.28s None ?
DQN - CartPole 10.61±5.51s 1046.34±291.27s 40.16±12.79s 175.55±53.81s ?
A2C - CartPole 11.72±3.85s *(~1612s) 46.15±6.64s Runtime Error ?
PPO - CartPole 35.25±16.47s *(~1179s) 62.21±13.31s (APPO) 29.16±15.46s ?
DDPG - Pendulum 46.95±24.31s *(>1h) 377.99±13.79s 652.83±471.28s 172.18±62.48s
TD3 - Pendulum 48.39±7.22s None 620.83±248.43s 619.33±324.97s 210.31±76.30s
SAC - Pendulum 38.92±2.09s None 92.68±4.48s 808.21±405.70s 295.92±140.85s

*: Could not reach the target reward threshold in 1e6 steps in any of 10 runs. The total runtime is in the brackets.

?: We have tried but it is nontrivial for running non-Atari game on rlpyt. See here.

All of the platforms use 10 different seeds for testing. We erase those trials which failed for training. The reward threshold is 195.0 in CartPole and -250.0 in Pendulum over consecutive 100 episodes' mean returns.

Tianshou and RLlib's configures are very similar. They both use multiple workers for sampling. Indeed, both RLlib and rlpyt are excellent reinforcement learning platform.

We will add results of Atari Pong / Mujoco these days.


Tianshou has unit tests. Different from other platforms, the unit tests include the full agent training procedure for all of the implemented algorithms. It will be failed once it cannot train an agent to perform well enough on limited epochs on toy scenarios. The unit tests secure the reproducibility of our platform.

Check out the GitHub Actions page for more detail.

Modularized Policy

We decouple all of the algorithms into 4 parts:

  • __init__: initialize the policy;
  • process_fn: to preprocess data from replay buffer (since we have reformulated all algorithms to replay-buffer based algorithms);
  • __call__: to compute actions over given observations;
  • learn: to learn from a given batch data.

Within these API, we can interact with different policies conveniently.

Elegant and Flexible

Currently, the overall code of Tianshou platform is less than 1500 lines. Most of the implemented algorithms are less than 100 lines of python code. It is quite easy to go through the framework and understand how it works. We provide many flexible API as you wish, for instance, if you want to use your policy to interact with environment with n steps:

result = collector.collect(n_step=n)

If you have 3 environment in total and want to collect 1 episode in the first environment, 3 for third environment:

result = collector.collect(n_episode=[1, 0, 3])

If you want to train the given policy with a sampled batch:

result = policy.learn(collector.sample(batch_size))

You can check out the documentation for further usage.

Quick Start

This is an example of Deep Q Network. You can also run the full script at test/discrete/test_dqn.py.

First, import some relevant packages:

import gym, torch, numpy as np, torch.nn as nn
from torch.utils.tensorboard import SummaryWriter
import tianshou as ts

Define some hyper-parameters:

task = 'CartPole-v0'
lr = 1e-3
gamma = 0.9
n_step = 3
eps_train, eps_test = 0.1, 0.05
epoch = 10
step_per_epoch = 1000
collect_per_step = 10
target_freq = 320
batch_size = 64
train_num, test_num = 8, 100
buffer_size = 20000
writer = SummaryWriter('log/dqn')  # tensorboard is also supported!

Make environments:

# you can also try with SubprocVectorEnv
train_envs = ts.env.VectorEnv([lambda: gym.make(task) for _ in range(train_num)])
test_envs = ts.env.VectorEnv([lambda: gym.make(task) for _ in range(test_num)])

Define the network:

class Net(nn.Module):
    def __init__(self, state_shape, action_shape):
        self.model = nn.Sequential(*[
            nn.Linear(np.prod(state_shape), 128), nn.ReLU(inplace=True),
            nn.Linear(128, 128), nn.ReLU(inplace=True),
            nn.Linear(128, 128), nn.ReLU(inplace=True),
            nn.Linear(128, np.prod(action_shape))
    def forward(self, s, state=None, info={}):
        if not isinstance(s, torch.Tensor):
            s = torch.tensor(s, dtype=torch.float)
        batch = s.shape[0]
        logits = self.model(s.view(batch, -1))
        return logits, state

env = gym.make(task)
state_shape = env.observation_space.shape or env.observation_space.n
action_shape = env.action_space.shape or env.action_space.n
net = Net(state_shape, action_shape)
optim = torch.optim.Adam(net.parameters(), lr=lr)

Setup policy and collectors:

policy = ts.policy.DQNPolicy(net, optim, gamma, n_step,
    use_target_network=True, target_update_freq=target_freq)
train_collector = ts.data.Collector(policy, train_envs, ts.data.ReplayBuffer(buffer_size))
test_collector = ts.data.Collector(policy, test_envs)

Let's train it:

result = ts.trainer.offpolicy_trainer(
    policy, train_collector, test_collector, epoch, step_per_epoch, collect_per_step,
    test_num, batch_size, train_fn=lambda e: policy.set_eps(eps_train),
    test_fn=lambda e: policy.set_eps(eps_test),
    stop_fn=lambda x: x >= env.spec.reward_threshold, writer=writer, task=task)
print(f'Finished training! Use {result["duration"]}')

Save / load the trained policy (it's exactly the same as PyTorch nn.module):

torch.save(policy.state_dict(), 'dqn.pth')

Watch the performance with 35 FPS:

collector = ts.data.Collector(policy, env)
collector.collect(n_episode=1, render=1 / 35)

Look at the result saved in tensorboard: (on bash script)

tensorboard --logdir log/dqn

Citing Tianshou

If you find Tianshou useful, please cite it in your publications.

  author = {Jiayi Weng, Minghao Zhang},
  title = {Tianshou},
  year = {2020},
  publisher = {GitHub},
  journal = {GitHub repository},
  howpublished = {\url{https://github.com/thu-ml/tianshou}},


  • [x] More examples on [mujoco, atari] benchmark
  • [ ] Prioritized replay buffer
  • [ ] RNN support
  • [ ] Imitation Learning
  • [ ] Multi-agent
  • [ ] Distributed training