class_docstr: One-vs-one multiclass strategy.
  
  This strategy consists in fitting one classifier per class pair.
  At prediction time, the class which received the most votes is selected.
  Since it requires to fit `n_classes * (n_classes - 1) / 2` classifiers,
  this method is usually slower than one-vs-the-rest, due to its
  O(n_classes^2) complexity. However, this method may be advantageous for
  algorithms such as kernel algorithms which don't scale well with
  `n_samples`. This is because each individual learning problem only involves
  a small subset of the data whereas, with one-vs-the-rest, the complete
  dataset is used `n_classes` times.
  
  Read more in the :ref:`User Guide <ovo_classification>`.
  
  Parameters
  ----------
  estimator : estimator object
      A regressor or a classifier that implements :term:`fit`.
      When a classifier is passed, :term:`decision_function` will be used
      in priority and it will fallback to :term:`predict_proba` if it is not
      available.
      When a regressor is passed, :term:`predict` is used.
  
  n_jobs : int, default=None
      The number of jobs to use for the computation: the `n_classes * (
      n_classes - 1) / 2` OVO problems are computed in parallel.
  
      ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context.
      ``-1`` means using all processors. See :term:`Glossary <n_jobs>`
      for more details.
  
  Attributes
  ----------
  estimators_ : list of ``n_classes * (n_classes - 1) / 2`` estimators
      Estimators used for predictions.
  
  classes_ : numpy array of shape [n_classes]
      Array containing labels.
  
  n_classes_ : int
      Number of classes.
  
  pairwise_indices_ : list, length = ``len(estimators_)``, or ``None``
      Indices of samples used when training the estimators.
      ``None`` when ``estimator``'s `pairwise` tag is False.
  
  n_features_in_ : int
      Number of features seen during :term:`fit`.
  
      .. versionadded:: 0.24
  
  feature_names_in_ : ndarray of shape (`n_features_in_`,)
      Names of features seen during :term:`fit`. Defined only when `X`
      has feature names that are all strings.
  
      .. versionadded:: 1.0
  
  See Also
  --------
  OneVsRestClassifier : One-vs-all multiclass strategy.
  OutputCodeClassifier : (Error-Correcting) Output-Code multiclass strategy.
  
  Examples
  --------
  >>> from sklearn.datasets import load_iris
  >>> from sklearn.model_selection import train_test_split
  >>> from sklearn.multiclass import OneVsOneClassifier
  >>> from sklearn.svm import LinearSVC
  >>> X, y = load_iris(return_X_y=True)
  >>> X_train, X_test, y_train, y_test = train_test_split(
  ...     X, y, test_size=0.33, shuffle=True, random_state=0)
  >>> clf = OneVsOneClassifier(
  ...     LinearSVC(dual="auto", random_state=0)).fit(X_train, y_train)
  >>> clf.predict(X_test[:10])
  array([2, 1, 0, 2, 0, 2, 0, 1, 1, 1])
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docstr: Partially fit underlying estimators.
  
  Should be used when memory is inefficient to train all data. Chunks
  of data can be passed in several iteration, where the first call
  should have an array of all target variables.
  
  Parameters
  ----------
  X : {array-like, sparse matrix) of shape (n_samples, n_features)
      Data.
  
  y : array-like of shape (n_samples,)
      Multi-class targets.
  
  classes : array, shape (n_classes, )
      Classes across all calls to partial_fit.
      Can be obtained via `np.unique(y_all)`, where y_all is the
      target vector of the entire dataset.
      This argument is only required in the first call of partial_fit
      and can be omitted in the subsequent calls.
  
  Returns
  -------
  self : object
      The partially fitted underlying estimator.
code: def partial_fit(self, X, y, classes=None):
      """Partially fit underlying estimators.
  
      Should be used when memory is inefficient to train all data. Chunks
      of data can be passed in several iteration, where the first call
      should have an array of all target variables.
  
      Parameters
      ----------
      X : {array-like, sparse matrix) of shape (n_samples, n_features)
          Data.
  
      y : array-like of shape (n_samples,)
          Multi-class targets.
  
      classes : array, shape (n_classes, )
          Classes across all calls to partial_fit.
          Can be obtained via `np.unique(y_all)`, where y_all is the
          target vector of the entire dataset.
          This argument is only required in the first call of partial_fit
          and can be omitted in the subsequent calls.
  
      Returns
      -------
      self : object
          The partially fitted underlying estimator.
      """
      first_call = _check_partial_fit_first_call(self, classes)
      if first_call:
          self.estimators_ = [
              clone(self.estimator)
              for _ in range(
                  self.n_classes_ * (self.n_classes_ - 1) // 2
              )
          ]
  
      if len(np.setdiff1d(y, self.classes_)):
          raise ValueError(
              "Mini-batch contains {0} while it must be subset of {1}".format(
                  np.unique(y), self.classes_
              )
          )
  
      X, y = self._validate_data(
          X,
          y,
          accept_sparse=["csr", "csc"],
          force_all_finite=False,
          reset=first_call,
      )
      check_classification_targets(y)
      combinations = itertools.combinations(range(self.n_classes_), 2)
      self.estimators_ = Parallel(n_jobs=self.n_jobs)(
          delayed(_partial_fit_ovo_binary)(
              estimator, X, y, self.classes_[i], self.classes_[j]
          )
          for estimator, (i, j) in zip(self.estimators_, (combinations))
      )
  
      self.pairwise_indices_ = None
  
      if hasattr(self.estimators_[0], "n_features_in_"):
          self.n_features_in_ = self.estimators_[0].n_features_in_
  
      return self
  
imports: import array
  import itertools
  import warnings
  from numbers import Integral, Real
  import numpy
  import scipy.sparse
  from .base import BaseEstimator, ClassifierMixin, MetaEstimatorMixin, MultiOutputMixin, _fit_context, clone, is_classifier, is_regressor
  from .metrics.pairwise import pairwise_distances_argmin
  from .preprocessing import LabelBinarizer
  from .utils import check_random_state
  from .utils._param_validation import HasMethods, Interval
  from .utils._tags import _safe_tags
  from .utils.metaestimators import _safe_split, available_if
  from .utils.multiclass import _check_partial_fit_first_call, _ovr_decision_function, check_classification_targets
  from .utils.parallel import Parallel, delayed
  from .utils.validation import _num_samples, check_is_fitted
label_desc: Use image node_id 3 for calling the OneVsOneClassifier obj's underlying member method code with example usage: obj.partial_fit(X, y, classes) and returns: self