OpenAI's Gym binding for Julia



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Author: Thomas Breloff (@tbreloff)

This wraps the open source python library gym, released by OpenAI. See their website for more information. Collaboration welcome!


Install gym

First install gym. If you use Python on your system, and wish to use the same installation of gym in both Python and Julia, follow the system-wide instructions. If you only need gym within Julia, follow the Julia-specific instructions.

  1. System-wide Python

    Install gym into Python, following the instructions here.

    In Julia, ensure that the Python environment variable points to the correct executable, and build PyCall:

    julia> ENV["PYTHON"] = "... path of the python executable ..."
    julia> # ENV["PYTHON"] = "C:\\Python37-x64\\python.exe" # example for Windows
    julia> # ENV["PYTHON"] = "/usr/bin/python3.7"           # example for *nix/Mac
    julia> Pkg.build("PyCall")

    Finally, re-launch Julia.

  2. Julia-specific Python

    Julia also has its own miniconda installation of Python, via Conda.jl:

    using Pkg
    withenv("PYTHON" => "") do

    then install gym from the command line:

    ~/.julia/conda/3/bin/pip install 'gym[all]==0.11.0'

    We only test with gym v0.11.0 at this moment.

Install OpenAIGym.jl

julia> using Pkg

julia> Pkg.add("https://github.com/JuliaML/OpenAIGym.jl.git")

Hello world!

using OpenAIGym
env = GymEnv(:CartPole, :v0)
for i ∈ 1:20
  T = 0
  R = run_episode(env, RandomPolicy()) do (s, a, r, s′)
    T += 1
  @info("Episode $i finished after $T steps. Total reward: $R")

(The character is a prime; if using the REPL, type \prime.) If everything works you should see output like this:

[ Info: Episode 1 finished after 10 steps. Total reward: 10.0
[ Info: Episode 2 finished after 46 steps. Total reward: 46.0
[ Info: Episode 3 finished after 14 steps. Total reward: 14.0
[ Info: Episode 4 finished after 19 steps. Total reward: 19.0
[ Info: Episode 5 finished after 15 steps. Total reward: 15.0
[ Info: Episode 6 finished after 32 steps. Total reward: 32.0
[ Info: Episode 7 finished after 36 steps. Total reward: 36.0
[ Info: Episode 8 finished after 13 steps. Total reward: 13.0
[ Info: Episode 9 finished after 62 steps. Total reward: 62.0
[ Info: Episode 10 finished after 14 steps. Total reward: 14.0
[ Info: Episode 11 finished after 14 steps. Total reward: 14.0
[ Info: Episode 12 finished after 28 steps. Total reward: 28.0
[ Info: Episode 13 finished after 21 steps. Total reward: 21.0
[ Info: Episode 14 finished after 15 steps. Total reward: 15.0
[ Info: Episode 15 finished after 12 steps. Total reward: 12.0
[ Info: Episode 16 finished after 20 steps. Total reward: 20.0
[ Info: Episode 17 finished after 19 steps. Total reward: 19.0
[ Info: Episode 18 finished after 17 steps. Total reward: 17.0
[ Info: Episode 19 finished after 35 steps. Total reward: 35.0
[ Info: Episode 20 finished after 23 steps. Total reward: 23.0

Note: this is equivalent to the python code:

import gym
env = gym.make('CartPole-v0')
for i_episode in xrange(20):
    total_reward = 0.0
    observation = env.reset()
    for t in xrange(100):
        # env.render()
        # print observation
        action = env.action_space.sample()
        observation, reward, done, info = env.step(action)
        total_reward += reward
        if done:
            print "Episode {} finished after {} timesteps. Total reward: {}".format(i_episode, t+1, total_reward)

We're using the RandomPolicy from Reinforce.jl. To do something better, you can create your own policy simply by implementing the action method, which takes a reward, a state, and an action set, then returns an action selection:

type RandomPolicy <: AbstractPolicy end
Reinforce.action(policy::AbstractPolicy, r, s, A) = rand(A)

Note: You can override default behavior of in the run_episode method. Just iterate yourself:

ep = Episode(env, policy)
for (s, a, r, s′) in ep
    # do something special?
R = ep.total_reward
N = ep.niter

First Commit


Last Touched

10 days ago


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