code: def kernel(request, backend):
      """
      Gaussian RBF kernel for given backend. Settings are parametrised in the test function.
      """
      kernel = request.param
  
      if isinstance(kernel, dict):  # dict of kwargs
          kernel_cfg = kernel.copy()
          sigma = kernel_cfg.pop("sigma", None)
          if backend == "tensorflow":
              if sigma is not None and not isinstance(sigma, tf.Tensor):
                  sigma = tf.convert_to_tensor(sigma)
              kernel = GaussianRBF_tf(sigma=sigma, **kernel_cfg)
          elif backend == "pytorch":
              if sigma is not None and not isinstance(
                  sigma, torch.Tensor
              ):
                  sigma = torch.tensor(sigma)
              kernel = GaussianRBF_pt(sigma=sigma, **kernel_cfg)
          elif backend == "keops":
              if sigma is not None and not isinstance(
                  sigma, torch.Tensor
              ):
                  sigma = torch.tensor(sigma)
              kernel = GaussianRBF_ke(sigma=sigma, **kernel_cfg)
          else:
              pytest.skip(
                  "`kernel` only implemented for tensorflow, pytorch and keops."
              )
      return kernel
  
imports: from functools import partial
  from importlib import import_module
  import numpy
  import tensorflow
  import torch
  import torch.nn
  from sklearn.ensemble import RandomForestClassifier
  from xgboost import XGBClassifier
  from requests.exceptions import HTTPError
  import pytest
  from pytest_cases import fixture, parametrize
  from transformers import AutoTokenizer
  from alibi_detect.cd.pytorch import UAE
  from alibi_detect.cd.pytorch import preprocess_drift
  from alibi_detect.cd.tensorflow import UAE
  from alibi_detect.cd.tensorflow import preprocess_drift
  from alibi_detect.utils.pytorch.kernels import GaussianRBF
  from alibi_detect.utils.pytorch.kernels import DeepKernel
  from alibi_detect.utils.tensorflow.kernels import GaussianRBF
  from alibi_detect.utils.tensorflow.kernels import DeepKernel
  from alibi_detect.models.pytorch import TransformerEmbedding
  from alibi_detect.models.tensorflow import TransformerEmbedding
  from alibi_detect.cd.pytorch import HiddenOutput
  from alibi_detect.cd.tensorflow import HiddenOutput
  from alibi_detect.utils.frameworks import has_keops
label_desc: Use image node_id 4 for calling a global function with example usage: kernel(request, backend) and returns: kernel