Callbacks¶
A callback is a set of functions that will be called at given stages of the training procedure. You can use callbacks to access internal state of the RL model during training. It allows one to do monitoring, auto saving, model manipulation, progress bars, …
Custom Callback¶
To build a custom callback, you need to create a class that derives from BaseCallback
.
This will give you access to events (_on_training_start
, _on_step
) and useful variables (like self.model for the RL model).
You can find two examples of custom callbacks in the documentation: one for saving the best model according to the training reward (see Examples), and one for logging additional values with Tensorboard (see Tensorboard section).
from stable_baselines3.common.callbacks import BaseCallback
class CustomCallback(BaseCallback):
"""
A custom callback that derives from ``BaseCallback``.
:param verbose: (int) Verbosity level 0: not output 1: info 2: debug
"""
def __init__(self, verbose=0):
super(CustomCallback, self).__init__(verbose)
# Those variables will be accessible in the callback
# (they are defined in the base class)
# The RL model
# self.model = None # type: BaseAlgorithm
# An alias for self.model.get_env(), the environment used for training
# self.training_env = None # type: Union[gym.Env, VecEnv, None]
# Number of time the callback was called
# self.n_calls = 0 # type: int
# self.num_timesteps = 0 # type: int
# local and global variables
# self.locals = None # type: Dict[str, Any]
# self.globals = None # type: Dict[str, Any]
# The logger object, used to report things in the terminal
# self.logger = None # stable_baselines3.common.logger
# # Sometimes, for event callback, it is useful
# # to have access to the parent object
# self.parent = None # type: Optional[BaseCallback]
def _on_training_start(self) -> None:
"""
This method is called before the first rollout starts.
"""
pass
def _on_rollout_start(self) -> None:
"""
A rollout is the collection of environment interaction
using the current policy.
This event is triggered before collecting new samples.
"""
pass
def _on_step(self) -> bool:
"""
This method will be called by the model after each call to `env.step()`.
For child callback (of an `EventCallback`), this will be called
when the event is triggered.
:return: (bool) If the callback returns False, training is aborted early.
"""
return True
def _on_rollout_end(self) -> None:
"""
This event is triggered before updating the policy.
"""
pass
def _on_training_end(self) -> None:
"""
This event is triggered before exiting the `learn()` method.
"""
pass
Note
self.num_timesteps
corresponds to the total number of steps taken in the environment, i.e., it is the number of environments multiplied by the number of time env.step()
was called
For the other algorithms, self.num_timesteps
is incremented by n_envs
(number of environments) after each call to env.step()
Note
For off-policy algorithms like SAC, DDPG, TD3 or DQN, the notion of rollout
corresponds to the steps taken in the environment between two updates.
Event Callback¶
Compared to Keras, Stable Baselines provides a second type of BaseCallback
, named EventCallback
that is meant to trigger events. When an event is triggered, then a child callback is called.
As an example, EvalCallback is an EventCallback
that will trigger its child callback when there is a new best model.
A child callback is for instance StopTrainingOnRewardThreshold that stops the training if the mean reward achieved by the RL model is above a threshold.
Note
We recommend to take a look at the source code of EvalCallback and StopTrainingOnRewardThreshold to have a better overview of what can be achieved with this kind of callbacks.
class EventCallback(BaseCallback):
"""
Base class for triggering callback on event.
:param callback: (Optional[BaseCallback]) Callback that will be called
when an event is triggered.
:param verbose: (int)
"""
def __init__(self, callback: Optional[BaseCallback] = None, verbose: int = 0):
super(EventCallback, self).__init__(verbose=verbose)
self.callback = callback
# Give access to the parent
if callback is not None:
self.callback.parent = self
...
def _on_event(self) -> bool:
if self.callback is not None:
return self.callback()
return True
Callback Collection¶
Stable Baselines provides you with a set of common callbacks for:
saving the model periodically (CheckpointCallback)
evaluating the model periodically and saving the best one (EvalCallback)
chaining callbacks (CallbackList)
triggering callback on events (Event Callback, EveryNTimesteps)
stopping the training early based on a reward threshold (StopTrainingOnRewardThreshold)
CheckpointCallback¶
Callback for saving a model every save_freq
steps, you must specify a log folder (save_path
)
and optionally a prefix for the checkpoints (rl_model
by default).
from stable_baselines3 import SAC
from stable_baselines3.common.callbacks import CheckpointCallback
# Save a checkpoint every 1000 steps
checkpoint_callback = CheckpointCallback(save_freq=1000, save_path='./logs/',
name_prefix='rl_model')
model = SAC('MlpPolicy', 'Pendulum-v0')
model.learn(2000, callback=checkpoint_callback)
EvalCallback¶
Evaluate periodically the performance of an agent, using a separate test environment.
It will save the best model if best_model_save_path
folder is specified and save the evaluations results in a numpy archive (evaluations.npz) if log_path
folder is specified.
Note
You can pass a child callback via the callback_on_new_best
argument. It will be triggered each time there is a new best model.
import gym
from stable_baselines3 import SAC
from stable_baselines3.common.callbacks import EvalCallback
# Separate evaluation env
eval_env = gym.make('Pendulum-v0')
# Use deterministic actions for evaluation
eval_callback = EvalCallback(eval_env, best_model_save_path='./logs/',
log_path='./logs/', eval_freq=500,
deterministic=True, render=False)
model = SAC('MlpPolicy', 'Pendulum-v0')
model.learn(5000, callback=eval_callback)
CallbackList¶
Class for chaining callbacks, they will be called sequentially.
Alternatively, you can pass directly a list of callbacks to the learn() method, it will be converted automatically to a CallbackList
.
import gym
from stable_baselines3 import SAC
from stable_baselines3.common.callbacks import CallbackList, CheckpointCallback, EvalCallback
checkpoint_callback = CheckpointCallback(save_freq=1000, save_path='./logs/')
# Separate evaluation env
eval_env = gym.make('Pendulum-v0')
eval_callback = EvalCallback(eval_env, best_model_save_path='./logs/best_model',
log_path='./logs/results', eval_freq=500)
# Create the callback list
callback = CallbackList([checkpoint_callback, eval_callback])
model = SAC('MlpPolicy', 'Pendulum-v0')
# Equivalent to:
# model.learn(5000, callback=[checkpoint_callback, eval_callback])
model.learn(5000, callback=callback)
StopTrainingOnRewardThreshold¶
Stop the training once a threshold in episodic reward (mean episode reward over the evaluations) has been reached (i.e., when the model is good enough). It must be used with the EvalCallback and use the event triggered by a new best model.
import gym
from stable_baselines3 import SAC
from stable_baselines3.common.callbacks import EvalCallback, StopTrainingOnRewardThreshold
# Separate evaluation env
eval_env = gym.make('Pendulum-v0')
# Stop training when the model reaches the reward threshold
callback_on_best = StopTrainingOnRewardThreshold(reward_threshold=-200, verbose=1)
eval_callback = EvalCallback(eval_env, callback_on_new_best=callback_on_best, verbose=1)
model = SAC('MlpPolicy', 'Pendulum-v0', verbose=1)
# Almost infinite number of timesteps, but the training will stop
# early as soon as the reward threshold is reached
model.learn(int(1e10), callback=eval_callback)
EveryNTimesteps¶
An Event Callback that will trigger its child callback every n_steps
timesteps.
Note
Because of the way PPO1
and TRPO
work (they rely on MPI), n_steps
is a lower bound between two events.
import gym
from stable_baselines3 import PPO
from stable_baselines3.common.callbacks import CheckpointCallback, EveryNTimesteps
# this is equivalent to defining CheckpointCallback(save_freq=500)
# checkpoint_callback will be triggered every 500 steps
checkpoint_on_event = CheckpointCallback(save_freq=1, save_path='./logs/')
event_callback = EveryNTimesteps(n_steps=500, callback=checkpoint_on_event)
model = PPO('MlpPolicy', 'Pendulum-v0', verbose=1)
model.learn(int(2e4), callback=event_callback)
StopTrainingOnMaxEpisodes¶
Stop the training upon reaching the maximum number of episodes, regardless of the model’s total_timesteps
value.
Also, presumes that, for multiple environments, the desired behavior is that the agent trains on each env for max_episodes
and in total for max_episodes * n_envs
episodes.
Note
For multiple environments, the agent will train for a total of max_episodes * n_envs
episodes.
However, it can’t be guaranteed that this training will occur for an exact number of max_episodes
per environment.
Thus, there is an assumption that, on average, each environment ran for max_episodes
.
from stable_baselines3 import A2C
from stable_baselines3.common.callbacks import StopTrainingOnMaxEpisodes
# Stops training when the model reaches the maximum number of episodes
callback_max_episodes = StopTrainingOnMaxEpisodes(max_episodes=5, verbose=1)
model = A2C('MlpPolicy', 'Pendulum-v0', verbose=1)
# Almost infinite number of timesteps, but the training will stop
# early as soon as the max number of episodes is reached
model.learn(int(1e10), callback=callback_max_episodes)
-
class
stable_baselines3.common.callbacks.
BaseCallback
(verbose=0)[source]¶ Base class for callback.
- Parameters
verbose (
int
) –
-
init_callback
(model)[source]¶ Initialize the callback by saving references to the RL model and the training environment for convenience.
- Return type
None
-
on_step
()[source]¶ This method will be called by the model after each call to
env.step()
.For child callback (of an
EventCallback
), this will be called when the event is triggered.- Return type
bool
- Returns
If the callback returns False, training is aborted early.
-
class
stable_baselines3.common.callbacks.
CallbackList
(callbacks)[source]¶ Class for chaining callbacks.
- Parameters
callbacks (
List
[BaseCallback
]) – A list of callbacks that will be called sequentially.
-
class
stable_baselines3.common.callbacks.
CheckpointCallback
(save_freq, save_path, name_prefix='rl_model', verbose=0)[source]¶ Callback for saving a model every
save_freq
steps- Parameters
save_freq (
int
) –save_path (
str
) – Path to the folder where the model will be saved.name_prefix (
str
) – Common prefix to the saved modelsverbose (
int
) –
-
class
stable_baselines3.common.callbacks.
ConvertCallback
(callback, verbose=0)[source]¶ Convert functional callback (old-style) to object.
- Parameters
callback (
Callable
[[Dict
[str
,Any
],Dict
[str
,Any
]],bool
]) –verbose (
int
) –
-
class
stable_baselines3.common.callbacks.
EvalCallback
(eval_env, callback_on_new_best=None, n_eval_episodes=5, eval_freq=10000, log_path=None, best_model_save_path=None, deterministic=True, render=False, verbose=1, warn=True)[source]¶ Callback for evaluating an agent.
- Parameters
eval_env (
Union
[Env
,VecEnv
]) – The environment used for initializationcallback_on_new_best (
Optional
[BaseCallback
]) – Callback to trigger when there is a new best model according to themean_reward
n_eval_episodes (
int
) – The number of episodes to test the agenteval_freq (
int
) – Evaluate the agent every eval_freq call of the callback.log_path (
Optional
[str
]) – Path to a folder where the evaluations (evaluations.npz
) will be saved. It will be updated at each evaluation.best_model_save_path (
Optional
[str
]) – Path to a folder where the best model according to performance on the eval env will be saved.deterministic (
bool
) – Whether the evaluation should use a stochastic or deterministic actions.render (
bool
) – Whether to render or not the environment during evaluationverbose (
int
) –warn (
bool
) – Passed toevaluate_policy
(warns ifeval_env
has not been wrapped with a Monitor wrapper)
-
class
stable_baselines3.common.callbacks.
EventCallback
(callback=None, verbose=0)[source]¶ Base class for triggering callback on event.
- Parameters
callback (
Optional
[BaseCallback
]) – Callback that will be called when an event is triggered.verbose (
int
) –
-
class
stable_baselines3.common.callbacks.
EveryNTimesteps
(n_steps, callback)[source]¶ Trigger a callback every
n_steps
timesteps- Parameters
n_steps (
int
) – Number of timesteps between two trigger.callback (
BaseCallback
) – Callback that will be called when the event is triggered.
-
class
stable_baselines3.common.callbacks.
StopTrainingOnMaxEpisodes
(max_episodes, verbose=0)[source]¶ Stop the training once a maximum number of episodes are played.
For multiple environments presumes that, the desired behavior is that the agent trains on each env for
max_episodes
and in total formax_episodes * n_envs
episodes.- Parameters
max_episodes (
int
) – Maximum number of episodes to stop training.verbose (
int
) – Select whether to print information about when training ended by reachingmax_episodes
-
class
stable_baselines3.common.callbacks.
StopTrainingOnRewardThreshold
(reward_threshold, verbose=0)[source]¶ Stop the training once a threshold in episodic reward has been reached (i.e. when the model is good enough).
It must be used with the
EvalCallback
.- Parameters
reward_threshold (
float
) – Minimum expected reward per episode to stop training.verbose (
int
) –