# optuna.trial.Trial

class optuna.trial.Trial(study, trial_id)[source]

A trial is a process of evaluating an objective function.

This object is passed to an objective function and provides interfaces to get parameter suggestion, manage the trial’s state, and set/get user-defined attributes of the trial.

Note that the direct use of this constructor is not recommended. This object is seamlessly instantiated and passed to the objective function behind the optuna.study.Study.optimize() method; hence library users do not care about instantiation of this object.

Parameters

Methods

 report(value, step) Report an objective function value for a given step. set_system_attr(key, value) Set system attributes to the trial. set_user_attr(key, value) Set user attributes to the trial. Suggest whether the trial should be pruned or not. suggest_categorical(name, choices) Suggest a value for the categorical parameter. suggest_discrete_uniform(name, low, high, q) Suggest a value for the discrete parameter. suggest_float(name, low, high, *[, step, log]) Suggest a value for the floating point parameter. suggest_int(name, low, high[, step, log]) Suggest a value for the integer parameter. suggest_loguniform(name, low, high) Suggest a value for the continuous parameter. suggest_uniform(name, low, high) Suggest a value for the continuous parameter.

Attributes

 datetime_start Return start datetime. distributions Return distributions of parameters to be optimized. number Return trial's number which is consecutive and unique in a study. params Return parameters to be optimized. system_attrs Return system attributes. user_attrs Return user attributes.
property datetime_start: Optional[datetime]

Return start datetime.

Returns

Datetime where the Trial started.

property distributions: Dict[str, BaseDistribution]

Return distributions of parameters to be optimized.

Returns

A dictionary containing all distributions.

property number: int

Return trial’s number which is consecutive and unique in a study.

Returns

A trial number.

property params: Dict[str, Any]

Return parameters to be optimized.

Returns

A dictionary containing all parameters.

report(value, step)[source]

Report an objective function value for a given step.

The reported values are used by the pruners to determine whether this trial should be pruned.

Please refer to BasePruner.

Note

The reported value is converted to float type by applying float() function internally. Thus, it accepts all float-like types (e.g., numpy.float32). If the conversion fails, a TypeError is raised.

Note

If this method is called multiple times at the same step in a trial, the reported value only the first time is stored and the reported values from the second time are ignored.

Note

report() does not support multi-objective optimization.

Example

Report intermediate scores of SGDClassifier training.

import numpy as np
from sklearn.datasets import load_iris
from sklearn.linear_model import SGDClassifier
from sklearn.model_selection import train_test_split

import optuna

X, y = load_iris(return_X_y=True)
X_train, X_valid, y_train, y_valid = train_test_split(X, y)

def objective(trial):
clf = SGDClassifier(random_state=0)
for step in range(100):
clf.partial_fit(X_train, y_train, np.unique(y))
intermediate_value = clf.score(X_valid, y_valid)
trial.report(intermediate_value, step=step)
if trial.should_prune():
raise optuna.TrialPruned()

return clf.score(X_valid, y_valid)

study = optuna.create_study(direction="maximize")
study.optimize(objective, n_trials=3)

Parameters
• value (float) – A value returned from the objective function.

• step (int) – Step of the trial (e.g., Epoch of neural network training). Note that pruners assume that step starts at zero. For example, MedianPruner simply checks if step is less than n_warmup_steps as the warmup mechanism. step must be a positive integer.

Return type

None

set_system_attr(key, value)[source]

Set system attributes to the trial.

Note that Optuna internally uses this method to save system messages such as failure reason of trials. Please use set_user_attr() to set users’ attributes.

Parameters
• key (str) – A key string of the attribute.

• value (Any) – A value of the attribute. The value should be JSON serializable.

Return type

None

set_user_attr(key, value)[source]

Set user attributes to the trial.

The user attributes in the trial can be access via optuna.trial.Trial.user_attrs().

See the recipe on User Attributes.

Example

Save fixed hyperparameters of neural network training.

import numpy as np
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.neural_network import MLPClassifier

import optuna

X, y = load_iris(return_X_y=True)
X_train, X_valid, y_train, y_valid = train_test_split(X, y, random_state=0)

def objective(trial):
trial.set_user_attr("BATCHSIZE", 128)
momentum = trial.suggest_float("momentum", 0, 1.0)
clf = MLPClassifier(
hidden_layer_sizes=(100, 50),
batch_size=trial.user_attrs["BATCHSIZE"],
momentum=momentum,
solver="sgd",
random_state=0,
)
clf.fit(X_train, y_train)

return clf.score(X_valid, y_valid)

study = optuna.create_study(direction="maximize")
study.optimize(objective, n_trials=3)
assert "BATCHSIZE" in study.best_trial.user_attrs.keys()
assert study.best_trial.user_attrs["BATCHSIZE"] == 128

Parameters
• key (str) – A key string of the attribute.

• value (Any) – A value of the attribute. The value should be JSON serializable.

Return type

None

should_prune()[source]

Suggest whether the trial should be pruned or not.

The suggestion is made by a pruning algorithm associated with the trial and is based on previously reported values. The algorithm can be specified when constructing a Study.

Note

If no values have been reported, the algorithm cannot make meaningful suggestions. Similarly, if this method is called multiple times with the exact same set of reported values, the suggestions will be the same.

Please refer to the example code in optuna.trial.Trial.report().

Note

should_prune() does not support multi-objective optimization.

Returns

A boolean value. If True, the trial should be pruned according to the configured pruning algorithm. Otherwise, the trial should continue.

Return type

bool

suggest_categorical(name, choices)[source]

Suggest a value for the categorical parameter.

The value is sampled from choices.

Example

Suggest a kernel function of SVC.

import numpy as np
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.svm import SVC

import optuna

X, y = load_iris(return_X_y=True)
X_train, X_valid, y_train, y_valid = train_test_split(X, y)

def objective(trial):
kernel = trial.suggest_categorical("kernel", ["linear", "poly", "rbf"])
clf = SVC(kernel=kernel, gamma="scale", random_state=0)
clf.fit(X_train, y_train)
return clf.score(X_valid, y_valid)

study = optuna.create_study(direction="maximize")
study.optimize(objective, n_trials=3)

Parameters
Return type

Union[None, bool, int, float, str]

Returns

A suggested value.

Parameters
Return type

Union[None, bool, int, float, str]

2. Pythonic Search Space tutorial describes more details and flexible usages.

suggest_discrete_uniform(name, low, high, q)[source]

Suggest a value for the discrete parameter.

The value is sampled from the range $$[\mathsf{low}, \mathsf{high}]$$, and the step of discretization is $$q$$. More specifically, this method returns one of the values in the sequence $$\mathsf{low}, \mathsf{low} + q, \mathsf{low} + 2 q, \dots, \mathsf{low} + k q \le \mathsf{high}$$, where $$k$$ denotes an integer. Note that $$high$$ may be changed due to round-off errors if $$q$$ is not an integer. Please check warning messages to find the changed values.

Parameters
• name (str) – A parameter name.

• low (float) – Lower endpoint of the range of suggested values. low is included in the range.

• high (float) – Upper endpoint of the range of suggested values. high is included in the range.

• q (float) – A step of discretization.

Returns

A suggested float value.

Return type

float

Warning

Deprecated in v3.0.0. This feature will be removed in the future. The removal of this feature is currently scheduled for v6.0.0, but this schedule is subject to change. See https://github.com/optuna/optuna/releases/tag/v3.0.0.

Use suggest_float() instead.

suggest_float(name, low, high, *, step=None, log=False)[source]

Suggest a value for the floating point parameter.

New in version 1.3.0.

Example

Suggest a momentum, learning rate and scaling factor of learning rate for neural network training.

import numpy as np
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.neural_network import MLPClassifier

import optuna

X, y = load_iris(return_X_y=True)
X_train, X_valid, y_train, y_valid = train_test_split(X, y, random_state=0)

def objective(trial):
momentum = trial.suggest_float("momentum", 0.0, 1.0)
learning_rate_init = trial.suggest_float(
"learning_rate_init", 1e-5, 1e-3, log=True
)
power_t = trial.suggest_float("power_t", 0.2, 0.8, step=0.1)
clf = MLPClassifier(
hidden_layer_sizes=(100, 50),
momentum=momentum,
learning_rate_init=learning_rate_init,
solver="sgd",
random_state=0,
power_t=power_t,
)
clf.fit(X_train, y_train)

return clf.score(X_valid, y_valid)

study = optuna.create_study(direction="maximize")
study.optimize(objective, n_trials=3)

Parameters
• name (str) – A parameter name.

• low (float) – Lower endpoint of the range of suggested values. low is included in the range. low must be less than or equal to high. If log is True, low must be larger than 0.

• high (float) – Upper endpoint of the range of suggested values. high is included in the range. high must be greater than or equal to low.

• step (Union[None, float]) –

A step of discretization.

Note

The step and log arguments cannot be used at the same time. To set the step argument to a float number, set the log argument to False.

• log (bool) –

A flag to sample the value from the log domain or not. If log is true, the value is sampled from the range in the log domain. Otherwise, the value is sampled from the range in the linear domain.

Note

The step and log arguments cannot be used at the same time. To set the log argument to True, set the step argument to None.

Returns

A suggested float value.

Return type

float

2. Pythonic Search Space tutorial describes more details and flexible usages.

suggest_int(name, low, high, step=1, log=False)[source]

Suggest a value for the integer parameter.

The value is sampled from the integers in $$[\mathsf{low}, \mathsf{high}]$$.

Example

Suggest the number of trees in RandomForestClassifier.

import numpy as np
from sklearn.datasets import load_iris
from sklearn.ensemble import RandomForestClassifier
from sklearn.model_selection import train_test_split

import optuna

X, y = load_iris(return_X_y=True)
X_train, X_valid, y_train, y_valid = train_test_split(X, y)

def objective(trial):
n_estimators = trial.suggest_int("n_estimators", 50, 400)
clf = RandomForestClassifier(n_estimators=n_estimators, random_state=0)
clf.fit(X_train, y_train)
return clf.score(X_valid, y_valid)

study = optuna.create_study(direction="maximize")
study.optimize(objective, n_trials=3)

Parameters
• name (str) – A parameter name.

• low (int) – Lower endpoint of the range of suggested values. low is included in the range. low must be less than or equal to high. If log is True, low must be larger than 0.

• high (int) – Upper endpoint of the range of suggested values. high is included in the range. high must be greater than or equal to low.

• step (int) –

A step of discretization.

Note

Note that $$\mathsf{high}$$ is modified if the range is not divisible by $$\mathsf{step}$$. Please check the warning messages to find the changed values.

Note

The method returns one of the values in the sequence $$\mathsf{low}, \mathsf{low} + \mathsf{step}, \mathsf{low} + 2 * \mathsf{step}, \dots, \mathsf{low} + k * \mathsf{step} \le \mathsf{high}$$, where $$k$$ denotes an integer.

Note

The step != 1 and log arguments cannot be used at the same time. To set the step argument $$\mathsf{step} \ge 2$$, set the log argument to False.

• log (bool) –

A flag to sample the value from the log domain or not.

Note

If log is true, at first, the range of suggested values is divided into grid points of width 1. The range of suggested values is then converted to a log domain, from which a value is sampled. The uniformly sampled value is re-converted to the original domain and rounded to the nearest grid point that we just split, and the suggested value is determined. For example, if low = 2 and high = 8, then the range of suggested values is [2, 3, 4, 5, 6, 7, 8] and lower values tend to be more sampled than higher values.

Note

The step != 1 and log arguments cannot be used at the same time. To set the log argument to True, set the step argument to 1.

Return type

int

2. Pythonic Search Space tutorial describes more details and flexible usages.

suggest_loguniform(name, low, high)[source]

Suggest a value for the continuous parameter.

The value is sampled from the range $$[\mathsf{low}, \mathsf{high})$$ in the log domain. When $$\mathsf{low} = \mathsf{high}$$, the value of $$\mathsf{low}$$ will be returned.

Parameters
• name (str) – A parameter name.

• low (float) – Lower endpoint of the range of suggested values. low is included in the range.

• high (float) – Upper endpoint of the range of suggested values. high is included in the range.

Returns

A suggested float value.

Return type

float

Warning

Deprecated in v3.0.0. This feature will be removed in the future. The removal of this feature is currently scheduled for v6.0.0, but this schedule is subject to change. See https://github.com/optuna/optuna/releases/tag/v3.0.0.

Use suggest_float() instead.

suggest_uniform(name, low, high)[source]

Suggest a value for the continuous parameter.

The value is sampled from the range $$[\mathsf{low}, \mathsf{high})$$ in the linear domain. When $$\mathsf{low} = \mathsf{high}$$, the value of $$\mathsf{low}$$ will be returned.

Parameters
• name (str) – A parameter name.

• low (float) – Lower endpoint of the range of suggested values. low is included in the range.

• high (float) – Upper endpoint of the range of suggested values. high is included in the range.

Returns

A suggested float value.

Return type

float

Warning

Deprecated in v3.0.0. This feature will be removed in the future. The removal of this feature is currently scheduled for v6.0.0, but this schedule is subject to change. See https://github.com/optuna/optuna/releases/tag/v3.0.0.

Use suggest_float() instead.

property system_attrs: Dict[str, Any]

Return system attributes.

Returns

A dictionary containing all system attributes.

property user_attrs: Dict[str, Any]

Return user attributes.

Returns

A dictionary containing all user attributes.