Discrete

class Discrete(*args, init_value=None, constrain_fn=None, **kwargs)[source]

Bases: Discrete

Extended discrete space with state tracking and constraint support.

This class extends gymnasium.spaces.Discrete to add state management and optional constraint validation. Unlike the standard discrete space, this version maintains a current value and supports rejection sampling via a custom constraint function.

Variables:

  • init_value (int) – The initial value for the space.

  • value (int) – The current value of the space.

  • constrain_fn (callable) – Optional function that returns True if a value satisfies custom constraints.

Example

Create a discrete space that only accepts even numbers:

space = Discrete(n=10, init_value=0, constrain_fn=lambda x: x % 2 == 0)
value = space.sample()  # Samples even number and updates space.value
space.reset()  # Resets space.value back to 0 (init_value)

Note

The sample() method uses rejection sampling when a constraint function is provided, which may impact performance for difficult constraints.

__init__(*args, init_value=None, constrain_fn=None, **kwargs)[source]

Initialize a Discrete space with state tracking.

Parameters:

  • *args – Positional arguments passed to gymnasium.spaces.Discrete.

  • init_value (int, optional) – Initial value for the space. Defaults to None.

  • constrain_fn (callable, optional) – Function that takes an int and returns True if the value satisfies custom constraints. Defaults to None.

  • **kwargs – Keyword arguments passed to gymnasium.spaces.Discrete.

check()[source]

Validate the current space value.

Checks if the current value is within the space bounds and satisfies the constraint function. Logs a warning if the constraint fails.

Returns:

True if the current value is valid, False otherwise.

Return type:

bool

contains(x)[source]

Check if value is valid and satisfies constraints.

Parameters:

x (int) – The value to check.

Returns:

True if x is within bounds and satisfies the constraint

function, False otherwise.

Return type:

bool

property init_value

The initial value of the space, returned by reset().

Type:

int

reset()[source]

Reset the space value to its initial value.

Sets the current value back to the init_value specified during initialization.

sample(*args, max_tries=1000, warn_after_s=5.0, set_value=True, **kwargs)[source]

Sample a random value using rejection sampling for constraints.

Repeatedly samples values until one satisfies the constraint function or max_tries is reached. Optionally updates the space’s current value.

Parameters:

  • *args – Positional arguments passed to gymnasium.spaces.Discrete.sample().

  • max_tries (int, optional) – Maximum number of sampling attempts before raising an error. Defaults to 1000.

  • warn_after_s (float, optional) – Time threshold in seconds after which to log a warning about slow sampling. Set to None to disable. Defaults to 5.0.

  • set_value (bool, optional) – Whether to update the space’s current value with the sampled value. Defaults to True.

  • **kwargs – Keyword arguments passed to gymnasium.spaces.Discrete.sample().

Returns:

A sampled value that satisfies the constraint function.

Return type:

int

Raises:

RuntimeError – If no valid sample is found after max_tries attempts.

property value

The current value of the space.

Type:

int