<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _getitem(self, key, validate=False):
 """Return specified page from cache or file."""

        key = int(key)
        pages = self.pages

        if key < 0:
            key %= len(self)
        elif self._indexed and key >= len(pages):
            raise IndexError('index out of range')

        if key < len(pages):
            page = pages[key]
            if self._cache:
                if not isinstance(page, inttypes):
                    if validate and validate != page.hash:
                        raise RuntimeError('page hash mismatch')
                    return page
            elif isinstance(page, (TiffPage, self._tiffpage)):
                if validate and validate != page.hash:
                    raise RuntimeError('page hash mismatch')
                return page

        self._seek(key)
        page = self._tiffpage(self.parent, index=key, keyframe=self._keyframe)
        if validate and validate != page.hash:
            raise RuntimeError('page hash mismatch')
        if self._cache:
            pages[key] = page
        return page