code: def _prefix_keys(dictionary: Dict[str, Number], prefix: str):
      """Return a dictionary with prefixed keys.
  
      Args:
        dictionary: dictionary to return a copy of.
        prefix: string to use as the prefix.
  
      Returns:
        Return a copy of the given dictionary whose keys are replaced by
        "{prefix}_{key}". If the prefix is the empty string it returns the given
        dictionary unchanged.
      """
      if prefix:
          dictionary = {
              f"{prefix}_{k}": v for k, v in dictionary.items()
          }
      return dictionary
  
file_path: acme/acme/utils/counting.py
imports: import threading
  import time
  from typing import Dict, Mapping, Optional, Union
  from acme import core
label_desc: Use image node_id 1 for calling a global function with example usage: _prefix_keys(dictionary, prefix) and returns: dictionary