code: def ensure_file(
      source: str, destination: str | None = None, comment: bool = True
  ) -> None:
      """
      Copy file to default location if it does not already exist
  
      This tries to move a default configuration file to a default location if
      if does not already exist.  It also comments out that file by default.
  
      This is to be used by downstream modules (like dask.distributed) that may
      have default configuration files that they wish to include in the default
      configuration path.
  
      Parameters
      ----------
      source : string, filename
          Source configuration file, typically within a source directory.
      destination : string, directory
          Destination directory. Configurable by ``DASK_CONFIG`` environment
          variable, falling back to ~/.config/dask.
      comment : bool, True by default
          Whether or not to comment out the config file when copying.
      """
      if destination is None:
          destination = PATH
  
      # destination is a file and already exists, never overwrite
      if os.path.isfile(destination):
          return
  
      # If destination is not an existing file, interpret as a directory,
      # use the source basename as the filename
      directory = destination
      destination = os.path.join(directory, os.path.basename(source))
  
      try:
          if not os.path.exists(destination):
              os.makedirs(directory, exist_ok=True)
  
              # Atomically create destination.  Parallel testing discovered
              # a race condition where a process can be busy creating the
              # destination while another process reads an empty config file.
              tmp = "%s.tmp.%d" % (destination, os.getpid())
              with open(source) as f:
                  lines = list(f)
  
              if comment:
                  lines = [
                      "# " + line
                      if line.strip() and not line.startswith("#")
                      else line
                      for line in lines
                  ]
  
              with open(tmp, "w") as f:
                  f.write("".join(lines))
  
              try:
                  os.rename(tmp, destination)
              except OSError:
                  os.remove(tmp)
      except OSError:
          pass
  
imports: from __future__ import annotations
  import ast
  import base64
  import builtins
  import json
  import os
  import site
  import sys
  import threading
  import warnings
  from collections.abc import Mapping, Sequence
  from typing import Any, Literal
  import yaml
  from dask.typing import no_default
label_desc: Use image node_id 8 for calling a global function with example usage: ensure_file(source, destination, comment) without return types