# coding: utf-8
# pylint: disable = invalid-name, W0105, C0301
"""Callbacks library."""
from __future__ import absolute_import
import collections
import warnings
from operator import gt, lt
from .compat import range_
class EarlyStopException(Exception):
"""Exception of early stopping."""
def __init__(self, best_iteration, best_score):
"""Create early stopping exception.
Parameters
----------
best_iteration : int
The best iteration stopped.
best_score : float
The score of the best iteration.
"""
super(EarlyStopException, self).__init__()
self.best_iteration = best_iteration
self.best_score = best_score
# Callback environment used by callbacks
CallbackEnv = collections.namedtuple(
"LightGBMCallbackEnv",
["model",
"params",
"iteration",
"begin_iteration",
"end_iteration",
"evaluation_result_list"])
def _format_eval_result(value, show_stdv=True):
"""Format metric string."""
if len(value) == 4:
return '%s\'s %s: %g' % (value[0], value[1], value[2])
elif len(value) == 5:
if show_stdv:
return '%s\'s %s: %g + %g' % (value[0], value[1], value[2], value[4])
else:
return '%s\'s %s: %g' % (value[0], value[1], value[2])
else:
raise ValueError("Wrong metric value")
[docs]def print_evaluation(period=1, show_stdv=True):
"""Create a callback that prints the evaluation results.
Parameters
----------
period : int, optional (default=1)
The period to print the evaluation results.
show_stdv : bool, optional (default=True)
Whether to show stdv (if provided).
Returns
-------
callback : function
The callback that prints the evaluation results every ``period`` iteration(s).
"""
def _callback(env):
if period > 0 and env.evaluation_result_list and (env.iteration + 1) % period == 0:
result = '\t'.join([_format_eval_result(x, show_stdv) for x in env.evaluation_result_list])
print('[%d]\t%s' % (env.iteration + 1, result))
_callback.order = 10
return _callback
[docs]def record_evaluation(eval_result):
"""Create a callback that records the evaluation history into ``eval_result``.
Parameters
----------
eval_result : dict
A dictionary to store the evaluation results.
Returns
-------
callback : function
The callback that records the evaluation history into the passed dictionary.
"""
if not isinstance(eval_result, dict):
raise TypeError('Eval_result should be a dictionary')
eval_result.clear()
def _init(env):
for data_name, _, _, _ in env.evaluation_result_list:
eval_result.setdefault(data_name, collections.defaultdict(list))
def _callback(env):
if not eval_result:
_init(env)
for data_name, eval_name, result, _ in env.evaluation_result_list:
eval_result[data_name][eval_name].append(result)
_callback.order = 20
return _callback
[docs]def reset_parameter(**kwargs):
"""Create a callback that resets the parameter after the first iteration.
Note
----
The initial parameter will still take in-effect on first iteration.
Parameters
----------
**kwargs : value should be list or function
List of parameters for each boosting round
or a customized function that calculates the parameter in terms of
current number of round (e.g. yields learning rate decay).
If list lst, parameter = lst[current_round].
If function func, parameter = func(current_round).
Returns
-------
callback : function
The callback that resets the parameter after the first iteration.
"""
def _callback(env):
new_parameters = {}
for key, value in kwargs.items():
if key in ['num_class', 'num_classes',
'boosting', 'boost', 'boosting_type',
'metric', 'metrics', 'metric_types']:
raise RuntimeError("cannot reset {} during training".format(repr(key)))
if isinstance(value, list):
if len(value) != env.end_iteration - env.begin_iteration:
raise ValueError("Length of list {} has to equal to 'num_boost_round'."
.format(repr(key)))
new_param = value[env.iteration - env.begin_iteration]
else:
new_param = value(env.iteration - env.begin_iteration)
if new_param != env.params.get(key, None):
new_parameters[key] = new_param
if new_parameters:
env.model.reset_parameter(new_parameters)
env.params.update(new_parameters)
_callback.before_iteration = True
_callback.order = 10
return _callback
[docs]def early_stopping(stopping_rounds, first_metric_only=False, verbose=True):
"""Create a callback that activates early stopping.
Note
----
Activates early stopping.
The model will train until the validation score stops improving.
Validation score needs to improve at least every ``early_stopping_rounds`` round(s)
to continue training.
Requires at least one validation data and one metric.
If there's more than one, will check all of them. But the training data is ignored anyway.
To check only the first metric set ``first_metric_only`` to True.
Parameters
----------
stopping_rounds : int
The possible number of rounds without the trend occurrence.
first_metric_only : bool, optional (default=False)
Whether to use only the first metric for early stopping.
verbose : bool, optional (default=True)
Whether to print message with early stopping information.
Returns
-------
callback : function
The callback that activates early stopping.
"""
best_score = []
best_iter = []
best_score_list = []
cmp_op = []
enabled = [True]
def _init(env):
enabled[0] = not any((boost_alias in env.params
and env.params[boost_alias] == 'dart') for boost_alias in ('boosting',
'boosting_type',
'boost'))
if not enabled[0]:
warnings.warn('Early stopping is not available in dart mode')
return
if not env.evaluation_result_list:
raise ValueError('For early stopping, '
'at least one dataset and eval metric is required for evaluation')
if verbose:
msg = "Training until validation scores don't improve for {} rounds."
print(msg.format(stopping_rounds))
for eval_ret in env.evaluation_result_list:
best_iter.append(0)
best_score_list.append(None)
if eval_ret[3]:
best_score.append(float('-inf'))
cmp_op.append(gt)
else:
best_score.append(float('inf'))
cmp_op.append(lt)
def _callback(env):
if not cmp_op:
_init(env)
if not enabled[0]:
return
for i in range_(len(env.evaluation_result_list)):
score = env.evaluation_result_list[i][2]
if best_score_list[i] is None or cmp_op[i](score, best_score[i]):
best_score[i] = score
best_iter[i] = env.iteration
best_score_list[i] = env.evaluation_result_list
elif env.iteration - best_iter[i] >= stopping_rounds:
if verbose:
print('Early stopping, best iteration is:\n[%d]\t%s' % (
best_iter[i] + 1, '\t'.join([_format_eval_result(x) for x in best_score_list[i]])))
raise EarlyStopException(best_iter[i], best_score_list[i])
if env.iteration == env.end_iteration - 1:
if verbose:
print('Did not meet early stopping. Best iteration is:\n[%d]\t%s' % (
best_iter[i] + 1, '\t'.join([_format_eval_result(x) for x in best_score_list[i]])))
raise EarlyStopException(best_iter[i], best_score_list[i])
if first_metric_only: # the only first metric is used for early stopping
break
_callback.order = 30
return _callback