code: def kernel_metrics():
      """Valid metrics for pairwise_kernels.
  
      This function simply returns the valid pairwise distance metrics.
      It exists, however, to allow for a verbose description of the mapping for
      each of the valid strings.
  
      The valid distance metrics, and the function they map to, are:
        ===============   ========================================
        metric            Function
        ===============   ========================================
        'additive_chi2'   sklearn.pairwise.additive_chi2_kernel
        'chi2'            sklearn.pairwise.chi2_kernel
        'linear'          sklearn.pairwise.linear_kernel
        'poly'            sklearn.pairwise.polynomial_kernel
        'polynomial'      sklearn.pairwise.polynomial_kernel
        'rbf'             sklearn.pairwise.rbf_kernel
        'laplacian'       sklearn.pairwise.laplacian_kernel
        'sigmoid'         sklearn.pairwise.sigmoid_kernel
        'cosine'          sklearn.pairwise.cosine_similarity
        ===============   ========================================
  
      Read more in the :ref:`User Guide <metrics>`.
  
      Returns
      -------
      kernel_metrics : dict
          Returns valid metrics for pairwise_kernels.
      """
      return PAIRWISE_KERNEL_FUNCTIONS
  
imports: import itertools
  import warnings
  from functools import partial
  import numpy
  from joblib import effective_n_jobs
  from scipy.sparse import csr_matrix, issparse
  from scipy.spatial import distance
  from ..None import config_context
  from ..exceptions import DataConversionWarning
  from ..preprocessing import normalize
  from ..utils import check_array, gen_batches, gen_even_slices, get_chunk_n_rows, is_scalar_nan
  from ..utils._mask import _get_mask
  from ..utils._param_validation import Hidden, Integral, Interval, MissingValues, Options, Real, StrOptions, validate_params
  from ..utils.extmath import row_norms, safe_sparse_dot
  from ..utils.fixes import parse_version, sp_base_version
  from ..utils.parallel import Parallel, delayed
  from ..utils.validation import _num_samples, check_non_negative
  from ._pairwise_distances_reduction import ArgKmin
  from ._pairwise_fast import _chi2_kernel_fast, _sparse_manhattan
label_desc: Use image node_id 35 for calling a global function with example usage: kernel_metrics() and returns: PAIRWISE_KERNEL_FUNCTIONS