<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def to_csv(self, fileobj=sys.stdout):
 """Write data on file fileobj using CSV format."""

        openclose = is_string(fileobj)

        if openclose:
            fileobj = open(fileobj, "w")

        for idx, section in enumerate(self.sections):
            fileobj.write(section.to_csvline(with_header=(idx == 0)))
        fileobj.flush()

        if openclose:
            fileobj.close()