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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 _getitem(self, key):
 """Return specified page of series from cache or file."""

        key = int(key)
        if key < 0:
            key %= self._len
        if len(self._pages) == 1 and 0 < key < self._len:
            index = self._pages[0].index
            return self.parent.pages._getitem(index + key)
        return self._pages[key]