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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tolineno(self):
 """The last line that this node appears on in the source code. :type: int or None """

        if not self._astroid_fields:
            # can't have children
            lastchild = None
        else:
            lastchild = self.last_child()
        if lastchild is None:
            return self.fromlineno

        return lastchild.tolineno