code: def check_environ():
      """Ensure that 'os.environ' has all the environment variables we
      guarantee that users can use in config files, command-line options,
      etc.  Currently this includes:
        HOME - user's home directory (Unix only)
        PLAT - description of the current platform, including hardware
               and OS (see 'get_platform()')
      """
      global _environ_checked
      if _environ_checked:
          return
  
      if os.name == "posix" and "HOME" not in os.environ:
          try:
              import pwd
  
              os.environ["HOME"] = pwd.getpwuid(os.getuid())[5]
          except (ImportError, KeyError):
              # bpo-10496: if the current user identifier doesn't exist in the
              # password database, do nothing
              pass
  
      if "PLAT" not in os.environ:
          os.environ["PLAT"] = get_platform()
  
      _environ_checked = 1
  
imports: import os
  import re
  import importlib.util
  import string
  import sys
  import distutils
  from distutils.errors import DistutilsPlatformError
  from distutils.dep_util import newer
  from distutils.spawn import spawn
  from distutils import log
  from distutils.errors import DistutilsByteCompileError
label_desc: Use image node_id 5 for calling a global function with example usage: check_environ() without return types