class_docstr: Core abstraction in modAL.
  
  Args:
      estimator: The estimator to be used in the active learning loop.
      query_strategy: Function providing the query strategy for the active learning loop,
          for instance, modAL.uncertainty.uncertainty_sampling.
      force_all_finite: When True, forces all values of the data finite.
          When False, accepts np.nan and np.inf values.
      on_transformed: Whether to transform samples with the pipeline defined by the estimator
          when applying the query strategy.
      **fit_kwargs: keyword arguments.
  
  Attributes:
      estimator: The estimator to be used in the active learning loop.
      query_strategy: Function providing the query strategy for the active learning loop.
code: def fit(self, *args, **kwargs) -> None:
      pass
  
imports: import abc
  import sys
  import warnings
  from typing import Any, Callable, Iterator, List, Tuple, Union
  import numpy
  import scipy.sparse
  from modAL.utils.data import data_hstack, modALinput, retrieve_rows
  from sklearn.base import BaseEstimator
  from sklearn.ensemble._base import _BaseHeterogeneousEnsemble
  from sklearn.pipeline import Pipeline
label_desc: Use image node_id 4 for calling the BaseLearner obj's underlying member method code with example usage: obj.fit() without return types