'Retrieve page number of a given PageObject
:param PageObject page: The page to get page number. Should be
an instance of :class:`PageObject<PyPDF2.pdf.PageObject>`
:return: the page number or -1 if page not found
:rtype: int'

def getPageNumber(self, page):

    indirectRef = page.indirectRef
    ret = self._getPageNumberByIndirect(indirectRef)
    return ret
