code: def main() -> None:
      """The command entry point."""
      parser = jupyter_parser()
      argv = sys.argv
      subcommand = None
      if "_ARGCOMPLETE" in os.environ:
          argv = _evaluate_argcomplete(parser)
          subcommand = argv[1]
      elif len(argv) > 1 and not argv[1].startswith("-"):
          # Don't parse if a subcommand is given
          # Avoids argparse gobbling up args passed to subcommand, such as `-h`.
          subcommand = argv[1]
      else:
          args, opts = parser.parse_known_args()
          subcommand = args.subcommand
          if args.version:
              print("Selected Jupyter core packages...")
              for package in [
                  "IPython",
                  "ipykernel",
                  "ipywidgets",
                  "jupyter_client",
                  "jupyter_core",
                  "jupyter_server",
                  "jupyterlab",
                  "nbclient",
                  "nbconvert",
                  "nbformat",
                  "notebook",
                  "qtconsole",
                  "traitlets",
              ]:
                  try:
                      if (
                          package == "jupyter_core"
                      ):  # We're already here
                          version = __version__
                      else:
                          mod = __import__(package)
                          version = mod.__version__
                  except ImportError:
                      version = "not installed"
                  print(f"{package:<17}:", version)
              return
          if args.json and not args.paths:
              sys.exit("--json is only used with --paths")
          if args.debug and not args.paths:
              sys.exit("--debug is only used with --paths")
          if args.debug and args.json:
              sys.exit("--debug cannot be used with --json")
          if args.config_dir:
              print(paths.jupyter_config_dir())
              return
          if args.data_dir:
              print(paths.jupyter_data_dir())
              return
          if args.runtime_dir:
              print(paths.jupyter_runtime_dir())
              return
          if args.paths:
              data = {}
              data["runtime"] = [paths.jupyter_runtime_dir()]
              data["config"] = paths.jupyter_config_path()
              data["data"] = paths.jupyter_path()
              if args.json:
                  print(json.dumps(data))
              else:
                  if args.debug:
                      env = os.environ
  
                      if paths.use_platform_dirs():
                          print(
                              "JUPYTER_PLATFORM_DIRS is set to a true value, so we use platformdirs to find platform-specific directories"
                          )
                      else:
                          print(
                              "JUPYTER_PLATFORM_DIRS is set to a false value, or is not set, so we use hardcoded legacy paths for platform-specific directories"
                          )
  
                      if paths.prefer_environment_over_user():
                          print(
                              "JUPYTER_PREFER_ENV_PATH is set to a true value, or JUPYTER_PREFER_ENV_PATH is not set and we detected a virtual environment, making the environment-level path preferred over the user-level path for data and config"
                          )
                      else:
                          print(
                              "JUPYTER_PREFER_ENV_PATH is set to a false value, or JUPYTER_PREFER_ENV_PATH is not set and we did not detect a virtual environment, making the user-level path preferred over the environment-level path for data and config"
                          )
  
                      # config path list
                      if env.get("JUPYTER_NO_CONFIG"):
                          print(
                              "JUPYTER_NO_CONFIG is set, making the config path list only a single temporary directory"
                          )
                      else:
                          print(
                              "JUPYTER_NO_CONFIG is not set, so we use the full path list for config"
                          )
  
                      if env.get("JUPYTER_CONFIG_PATH"):
                          print(
                              f"JUPYTER_CONFIG_PATH is set to '{env.get('JUPYTER_CONFIG_PATH')}', which is prepended to the config path list (unless JUPYTER_NO_CONFIG is set)"
                          )
                      else:
                          print(
                              "JUPYTER_CONFIG_PATH is not set, so we do not prepend anything to the config paths"
                          )
  
                      if env.get("JUPYTER_CONFIG_DIR"):
                          print(
                              f"JUPYTER_CONFIG_DIR is set to '{env.get('JUPYTER_CONFIG_DIR')}', overriding the default user-level config directory"
                          )
                      else:
                          print(
                              "JUPYTER_CONFIG_DIR is not set, so we use the default user-level config directory"
                          )
  
                      if site.ENABLE_USER_SITE:
                          print(
                              f"Python's site.ENABLE_USER_SITE is True, so we add the user site directory '{site.getuserbase()}'"
                          )
                      else:
                          print(
                              f"Python's site.ENABLE_USER_SITE is not True, so we do not add the Python site user directory '{site.getuserbase()}'"
                          )
  
                      # data path list
                      if env.get("JUPYTER_PATH"):
                          print(
                              f"JUPYTER_PATH is set to '{env.get('JUPYTER_PATH')}', which is prepended to the data paths"
                          )
                      else:
                          print(
                              "JUPYTER_PATH is not set, so we do not prepend anything to the data paths"
                          )
  
                      if env.get("JUPYTER_DATA_DIR"):
                          print(
                              f"JUPYTER_DATA_DIR is set to '{env.get('JUPYTER_DATA_DIR')}', overriding the default user-level data directory"
                          )
                      else:
                          print(
                              "JUPYTER_DATA_DIR is not set, so we use the default user-level data directory"
                          )
  
                      # runtime directory
                      if env.get("JUPYTER_RUNTIME_DIR"):
                          print(
                              f"JUPYTER_RUNTIME_DIR is set to '{env.get('JUPYTER_RUNTIME_DIR')}', overriding the default runtime directory"
                          )
                      else:
                          print(
                              "JUPYTER_RUNTIME_DIR is not set, so we use the default runtime directory"
                          )
  
                      print()
  
                  for name in sorted(data):
                      path = data[name]
                      print("%s:" % name)
                      for p in path:
                          print("    " + p)
              return
  
      if not subcommand:
          parser.print_help(file=sys.stderr)
          sys.exit(
              "\nPlease specify a subcommand or one of the optional arguments."
          )
  
      try:
          command = _jupyter_abspath(subcommand)
      except Exception as e:
          parser.print_help(file=sys.stderr)
          # special-case alias of "jupyter help" to "jupyter --help"
          if subcommand == "help":
              return
          sys.exit(str(e))
  
      try:
          _execvp(command, [command] + argv[2:])
      except OSError as e:
          sys.exit(
              f"Error executing Jupyter command {subcommand!r}: {e}"
          )
  
imports: from __future__ import annotations
  import argparse
  import errno
  import json
  import os
  import site
  import sys
  import sysconfig
  from pathlib import Path
  from shutil import which
  from subprocess import Popen
  from typing import Any
  from .None import paths
  from .version import __version__
label_desc: Use image node_id 7 for calling a global function with example usage: main() without return types