code: def totz(when, tz=None):
      
      if when is None:
          return None
      when = to_datetime(when)
      if when.tzinfo is None:
          when = when.replace(tzinfo=localtz)
      return when.astimezone(tz or utc)
docs: Return a date, time, or datetime converted to a datetime in the given timezone. If when is a
      datetime and has no timezone it is assumed to be local time. Date and time objects are also
      assumed to be UTC. The tz value defaults to UTC. Raise TypeError if when cannot be converted to
      a datetime.