<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def log_to_file(self, message):
 """Write a log message only to the file"""


        with self.build_fs.open(self.log_file, 'a+') as f:
            f.write(unicode(message + '\n'))