<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def __force_datetime(self, obj):
 """Converts ojb to time.datetime.datetime YAML parsing returns either date or datetime object depending on how the date is written. YYYY-MM-DD will return a date and YYYY-MM-DDThh:mm:ss will return a datetime :param obj: date or datetime object """

        if isinstance(obj, datetime.datetime):
            return obj

        t = datetime.time(0, 0)
        return datetime.datetime.combine(obj, t)