code: def _check_cb(cb_):
      '''
      If the callback is None or is not callable, return a lambda that returns
      the value passed.
      '''
      if cb_ is not None:
          if hasattr(cb_, '__call__'):
              return cb_
          else:
              log.error('log_callback is not callable, ignoring')
      return lambda x: f _check_cb(cb_):
      '''
      If the callback is None or is not callable, return a lambda that returns
      the value passed.
      '''
      if cb_ is not None:
          if hasattr(cb_, '__call__'):
              return cb_
          else:
              log.error('log_callback is not callable, ignoring')
      return lambda x: x
docs: If the callback is None or is not callable, return a lambda that returns
      the value passed.