code: def l2_norm(tree):
      """Computes the l2 norm of a pytree of arrays."""
      leaves = jax.tree_util.tree_leaves(tree)
      return jnp.sqrt(sum(jnp.vdot(x, x) for x in leaves))
  
imports: from typing import Any, Dict, List, Optional, Sequence, Tuple, Type, Union
  from absl import logging
  from clu import preprocess_spec
  from flax import core
  import jax
  import jax.numpy
  import numpy
  from scenic.train_lib import train_utils
  import scipy
label_desc: Use image node_id 8 for calling a global function with example usage: l2_norm(tree) and returns: jnp