class_docstr: A variable client for updating variables from a remote source.
docstr: Copies the new variables to the old ones.
code: def _copy(self, new_variables: Sequence[Sequence[tf.Variable]]):
      """Copies the new variables to the old ones."""
  
      new_variables = tree.flatten(new_variables)
      if len(self._variables) != len(new_variables):
          raise ValueError(
              "Length mismatch between old variables and new."
          )
  
      for new, old in zip(new_variables, self._variables):
          old.assign(new)
  
file_path: acme/acme/tf/variable_utils.py
imports: from concurrent import futures
  from typing import Mapping, Optional, Sequence
  from acme import core
  import tensorflow
  import tree
label_desc: Use image node_id 4 for calling the VariableClient obj's underlying member method code with example usage: obj._copy(new_variables) without return types