code: def get_config(
      key=None,
      default=None,
      raise_error=False,
      home_dir=None,
      use_env=True,
  ):
      """Read MNE-Python preferences from environment or config file.
  
      Parameters
      ----------
      key : None | str
          The preference key to look for. The os environment is searched first,
          then the mne-python config file is parsed.
          If None, all the config parameters present in environment variables or
          the path are returned. If key is an empty string, a list of all valid
          keys (but not values) is returned.
      default : str | None
          Value to return if the key is not found.
      raise_error : bool
          If True, raise an error if the key is not found (instead of returning
          default).
      home_dir : str | None
          The folder that contains the .mne config folder.
          If None, it is found automatically.
      use_env : bool
          If True, consider env vars, if available.
          If False, only use MNE-Python configuration file values.
  
          .. versionadded:: 0.18
  
      Returns
      -------
      value : dict | str | None
          The preference key value.
  
      See Also
      --------
      set_config
      """
      _validate_type(key, (str, type(None)), "key", "string or None")
  
      if key == "":
          # These are str->str (immutable) so we should just copy the dict
          # itself, no need for deepcopy
          return _known_config_types.copy()
  
      # first, check to see if key is in env
      if use_env and key is not None and key in os.environ:
          return os.environ[key]
  
      # second, look for it in mne-python config file
      config_path = get_config_path(home_dir=home_dir)
      if not op.isfile(config_path):
          config = {}
      else:
          config = _load_config(config_path)
  
      if key is None:
          # update config with environment variables
          if use_env:
              env_keys = (
                  set(config)
                  .union(_known_config_types)
                  .intersection(os.environ)
              )
              config.update({key: os.environ[key] for key in env_keys})
          return config
      elif raise_error is True and key not in config:
          loc_env = "the environment or in the " if use_env else ""
          meth_env = (
              (
                  'either os.environ["%s"] = VALUE for a temporary '
                  "solution, or " % key
              )
              if use_env
              else ""
          )
          extra_env = (
              " You can also set the environment variable before "
              "running python."
              if use_env
              else ""
          )
          meth_file = (
              'mne.utils.set_config("%s", VALUE, set_env=True) '
              "for a permanent one" % key
          )
          raise KeyError(
              'Key "%s" not found in %s'
              "the mne-python config file (%s). "
              "Try %s%s.%s"
              % (
                  key,
                  loc_env,
                  config_path,
                  meth_env,
                  meth_file,
                  extra_env,
              )
          )
      else:
          return config.get(key, default)
  
imports: import atexit
  import json
  import multiprocessing
  import os
  import os.path
  import platform
  import shutil
  import subprocess
  import sys
  import tempfile
  from functools import lru_cache, partial
  from importlib import import_module
  from pathlib import Path
  from urllib.error import URLError
  from urllib.request import urlopen
  from packaging.version import parse
  from ._logging import logger, warn
  from .check import _check_fname, _check_option, _check_qt_version, _validate_type
  from .docs import fill_doc
  from .misc import _pl
label_desc: Use image node_id 5 for calling a global function with example usage: get_config(key, default, raise_error, home_dir, use_env) and returns: _known_config_types, os, config, config