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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 _generate_ids(self, document, content):
 """Generate unique ids for html elements in page content so that it's possible to link to them. """

        existing_ids = content.xpath('//*/@id')
        elements = [
            'p', 'dl', 'dt', 'dd', 'table', 'div', 'section', 'figure',
            'blockquote', 'q', 'code', 'pre', 'object', 'img', 'audio',
            'video',
            ]
        elements_xpath = '|'.join(['.//{}|.//xhtml:{}'.format(elem, elem)
                                  for elem in elements])

        data_types = [
            'equation', 'list', 'exercise', 'rule', 'example', 'note',
            'footnote-number', 'footnote-ref', 'problem', 'solution', 'media',
            'proof', 'statement', 'commentary'
            ]
        data_types_xpath = '|'.join(['.//*[@data-type="{}"]'.format(data_type)
                                     for data_type in data_types])

        xpath = '|'.join([elements_xpath, data_types_xpath])

        mapping = {}  # old id -> new id

        for node in content.xpath(xpath, namespaces=HTML_DOCUMENT_NAMESPACES):
            old_id = node.attrib.get('id')
            document_id = document.id.replace('_', '')
            if old_id:
                new_id = 'auto_{}_{}'.format(document_id, old_id)
            else:
                random_number = random.randint(0, 100000)
                new_id = 'auto_{}_{}'.format(document_id, random_number)
            while new_id in existing_ids:
                random_number = random.randint(0, 100000)
                new_id = 'auto_{}_{}'.format(document_id, random_number)
            node.attrib['id'] = new_id
            if old_id:
                mapping[old_id] = new_id
            existing_ids.append(new_id)

        for a in content.xpath('//a[@href]|//xhtml:a[@href]',
                               namespaces=HTML_DOCUMENT_NAMESPACES):
            href = a.attrib['href']
            if href.startswith('#') and href[1:] in mapping:
                a.attrib['href'] = '#{}'.format(mapping[href[1:]])