code: def check_voms_proxy_validity(log=False):
      
      valid = _voms_proxy_info(["--exists"], silent=True)[0] == 0
      if log and not valid:
          logger.warning("no valid voms proxy found")
      return valid
docs: Returns *True* when a valid voms proxy exists, *False* otherwise. When *log* is *True*, a
      warning will be logged.