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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 offset(self):
 """Return offset to series data in file, if any."""

        if not self._pages:
            return None

        pos = 0
        for page in self._pages:
            if page is None:
                return None
            if not page.is_final:
                return None
            if not pos:
                pos = page.is_contiguous[0] + page.is_contiguous[1]
                continue
            if pos != page.is_contiguous[0]:
                return None
            pos += page.is_contiguous[1]

        page = self._pages[0]
        offset = page.is_contiguous[0]
        if (page.is_imagej or page.is_shaped) and len(self._pages) == 1:
            # truncated files
            return offset
        if pos == offset + product(self.shape) * self.dtype.itemsize:
            return offset
        return None