code: def init_reversible_blocks(blocks, loss_layer, input_signature, rng):
      """Initialize reversible blocks and the loss layer and place weights on CPU.
  
      Args:
        blocks: List of reversible blocks (pairs of layer lists).
        loss_layer: The final loss layer to initialize.
        input_signature: The signature of the input to the blocks.
        rng: Random key used to initialize the layers.
      """
      sig_stack = input_signature
      process = psutil.Process(os.getpid())
      mem_use = process.memory_info().rss
      for std_layers, rev_layers in blocks:
          rngs = fastmath.random.split(
              rng, len(std_layers) + len(rev_layers) + 1
          )
          rng = rngs[0]
          for layer, layer_rng in zip(
              std_layers + rev_layers, rngs[1:]
          ):
              sig = cb.inputs_from_stack(sig_stack, layer.n_in)
              layer.init(sig, rng=layer_rng)
              layer.weights = tl.on_cpu(
                  layer.weights
              )  # store weights in cpu memory
              layer.state = tl.on_cpu(
                  layer.state
              )  # store weights in cpu memory
              logging.info(
                  "init: layer %s\nadded cpu memory (MB): %.2f",
                  str(layer),
                  (process.memory_info().rss - mem_use)
                  / float(1024 * 1024),
              )
              mem_use = process.memory_info().rss
              logging.info(
                  "init: cpu memory use (MB): %.2f",
                  mem_use / float(1024 * 1024),
              )
              out_sig = layer.output_signature(sig)
              sig_stack = cb.outputs_onto_stack(
                  out_sig, sig_stack, layer.n_in
              )
      loss_layer.init(
          cb.inputs_from_stack(sig_stack, loss_layer.n_in), rng=rng
      )
      loss_layer.weights = tl.on_cpu(loss_layer.weights)
      loss_layer.state = tl.on_cpu(loss_layer.state)
  
imports: from concurrent import futures
  import functools
  import os
  import time
  from absl import logging
  import jax
  import numpy
  import psutil
  from trax import fastmath
  from trax import layers
  from trax.fastmath import numpy
  from trax.layers import base
  from trax.layers import combinators
label_desc: Use image node_id 8 for calling a global function with example usage: init_reversible_blocks(blocks, loss_layer, input_signature, rng) without return types