<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def setexternalfile(self, filename, offset=0):
 """Store the dataset data in an external file. Args:: filename external file name offset offset in bytes where to start writing in the external file Returns:: None C library equivalent : SDsetexternalfile """


        status = _C.SDsetexternalfile(self._id, filename, offset)
        _checkErr('setexternalfile', status, 'execution error')