code: def past_datetime(start='-30d'):
      
      return lambda n, f: f.past_datetime(
          start_date=start, tzinfo=get_timezone(),
      )
docs: Returns a ``datetime`` object in the past between 1 second ago and the
      specified ``start``. ``start`` can be a string, another datetime, or a
      timedelta. If it's a string, it must start with `-`, followed by and integer
      and a unit, Eg: ``'-30d'``. Defaults to `'-30d'`
  
      Valid units are:
      * ``'years'``, ``'y'``
      * ``'weeks'``, ``'w'``
      * ``'days'``, ``'d'``
      * ``'hours'``, ``'h'``
      * ``'minutes'``, ``'m'``
      * ``'seconds'``, ``'s'``