docs: def expanduser(path):
      """Expand ~ and ~user constructs.
  
      If user or $HOME is unknown, do nothing."""
      if path[:1] != '~':
          return path
      i, n = 1, len(path)
      while i < n and path[i] not in '/\\':
          i = i + 1
  
      if 'HOME' in os.environ:
          userhome = os.environ['HOME']
      elif 'USERPROFILE' in os.environ:
          userhome = os.environ['USERPROFILE']
      elif not 'HOMEPATH' in os.environ:
          return path
      else:
          try:
              drive = os.environ['HOMEDRIVE']
          except KeyError:
              drive = ''
          userhome = join(drive, os.environ['HOMEPATH'])
  
      if i != 1:  # ~user
          userhome = join(dirname(userhome), path[1:i])
  
      return userhome + path[i:]