code: def extract(self, X, y, n, is_x=True, is_train=True):
      if is_x:
          if self.pairwise:
              return self._extract_pairwise(X, y, n, is_train=is_train)
          return self._extract(X, y, n, is_x=True, is_train=is_train)
      if y is None:
          return None
      return self._extract(X, y, n, is_x=False, is_train=is_train)
  
imports: from __future__ import absolute_import, division, print_function
  import warnings
  from collections import defaultdict
  from threading import Lock
  from timeit import default_timer
  import numpy
  import packaging.version
  from dask.base import normalize_token
  from scipy import sparse
  from scipy.stats import rankdata
  from sklearn.exceptions import FitFailedWarning
  from sklearn.pipeline import FeatureUnion, Pipeline
  from sklearn.utils.validation import check_consistent_length
  from toolz import pluck
  from .._compat import Mapping
  from .utils import _index_param_value, _num_samples, _safe_indexing, copy_estimator
label_desc: Use image node_id 4 for calling the CVCache obj's underlying member method code with example usage: obj.extract(X, y, n, is_x, is_train) and returns: self, self, None, self