code: def backbone_scope(freeze):
      """
      Args:
          freeze (bool): whether to freeze all the variables under the scope
      """
  
      def nonlin(x):
          x = get_norm()(x)
          return tf.nn.relu(x)
  
      with argscope(
          [Conv2D, MaxPooling, BatchNorm], data_format="channels_first"
      ), argscope(
          Conv2D,
          use_bias=False,
          activation=nonlin,
          kernel_initializer=tfv1.variance_scaling_initializer(
              scale=2.0, mode="fan_out"
          ),
      ), ExitStack() as stack:
          if cfg.BACKBONE.NORM in ["FreezeBN", "SyncBN"]:
              if freeze or cfg.BACKBONE.NORM == "FreezeBN":
                  stack.enter_context(
                      argscope(BatchNorm, training=False)
                  )
              else:
                  stack.enter_context(
                      argscope(
                          BatchNorm,
                          sync_statistics="nccl"
                          if cfg.TRAINER == "replicated"
                          else "horovod",
                      )
                  )
  
          if freeze:
              stack.enter_context(
                  freeze_variables(
                      stop_gradient=False, skip_collection=True
                  )
              )
          else:
              # the layers are not completely freezed, but we may want to only freeze the affine
              if cfg.BACKBONE.FREEZE_AFFINE:
                  stack.enter_context(
                      custom_getter_scope(freeze_affine_getter)
                  )
          yield
  
imports: import numpy
  import tensorflow
  from contextlib import ExitStack, contextmanager
  from tensorpack import tfv1
  from tensorpack.models import BatchNorm, Conv2D, MaxPooling, layer_register
  from tensorpack.tfutils import argscope
  from tensorpack.tfutils.scope_utils import auto_reuse_variable_scope
  from tensorpack.tfutils.varreplace import custom_getter_scope, freeze_variables
  from config import config
label_desc: Use image node_id 4 for calling a global function with example usage: backbone_scope(freeze) and returns: tf