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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 get_chunk(self, obj):
 """Return the chunkattr of obj formatted with the chunkfomat specified in the constructor If the attr is None then ``None`` is returned not the string ``\'None\'``. :param obj: the fileinfo with information. :type obj: :class:`FileInfo` :returns: the chunk or None :rtype: str|None :raises: None """

        if self._chunkattr is None:
            return
        a = attrgetter(self._chunkattr)(obj)
        if a is None:
            return
        s = self._chunkformat % a
        return s