import re
content = """
Тема: Бла Бла Бла
Билет №1
1. валдывлдывладвылавыл
2. ldekldkldkldkld dkfdk
3. dkjkdjksdjdsjfdsj
Билет №2
1. вwdsалдывлдывладвылавыл
2. asdladekldkldkldkld dkfdk
3. dkjkdjksdjdsjfdsj
4. ldekldkldkldkld dkfdk
Билет №3
1. sadвwdsалд ывлдывлад вылавыл
2. asdsd ladekldkldkldkld dkfdk
3. asddkjkdjk sdjdsjfdsj
4. s ldekldkldksaldkld dkfdk
5. edk jkdjksdjdsjfdsj
Билет №4
1. sdsadвwdsалд ывлдывлад вылавыл
2. Dasdsd ladekldkldkldkld dkfdk
"""
ticket_num=3
print(re.search(fr'Билет №{ticket_num}(?:\n(?!\n).*)*', content).group())
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