code: def get_xdg_cache_dir():
      """Return the XDG_CACHE_HOME, if it is defined and exists, else None.
  
      This is only for non-OS X posix (Linux,Unix,etc.) systems.
      """
  
      env = os.environ
  
      if os.name == "posix" and sys.platform != "darwin":
          # Linux, Unix, AIX, etc.
          # use ~/.cache if empty OR not set
          xdg = env.get("XDG_CACHE_HOME", None) or os.path.join(
              get_home_dir(), ".cache"
          )
          if xdg and _writable_dir(xdg):
              return py3compat.cast_unicode(xdg, fs_encoding)
  
      return None
  
imports: import os
  import sys
  import errno
  import shutil
  import random
  import glob
  from warnings import warn
  from hashlib import md5
  from IPython.utils.process import system
  from IPython.utils import py3compat
  from IPython.utils.decorators import undoc
label_desc: Use image node_id 9 for calling a global function with example usage: get_xdg_cache_dir() and returns: None, py3compat