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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 popitem(self):
 """Removes the first key-value pair and return it. This method raises a ``KeyError`` if the list is empty. """

        node = self._head[2]
        if node is self._tail:
            raise KeyError('list is empty')
        self._find_lt(node[0])
        self._remove(node)
        return (node[0], node[1])