code: def from_rc(cls, rc=None):
      
      ret_vars = {}
      rc_locations = ['/etc/pexrc',
                      '~/.pexrc',
                      os.path.join(os.path.dirname(sys.argv[0]), '.pexrc')]
      if rc:
        rc_locations.append(rc)
      for filename in rc_locations:
        try:
          with open(os.path.expanduser(filename)) as fh:
            rc_items = map(cls._get_kv, fh)
            ret_vars.update(dict(filter(None, rc_items)))
        except IOError:
          continue
      return ret_vars
docs: Read pex runtime configuration variables from a pexrc file.
  
      :param rc: an absolute path to a pexrc file.
      :return: A dict of key value pairs found in processed pexrc files.
      :rtype: dict