code: def _diffable_kernel(x1, x2):
      """A differentiable kernel"""
      return qml.math.exp(-((x1 - x2) ** 2))
  
imports: import math
  import sys
  from functools import partial
  import pytest
  import numpy
  import pennylane
  import pennylane.kernels
  from pennylane import numpy
label_desc: Use image node_id 5 for calling a global function with example usage: _diffable_kernel(x1, x2) and returns: qml