how would you extract the "2021-12-30" from data-dat?
<td class="select_date" data-dat="2021-12-30" data-dat-f="30. Dec 2021" data-global-index="32" data-title="30.12.2021" id="d30-12-2021"><span class="bubble">30</span></td>
>Solution :
You can try attrs:
>>> soup.find("td").attrs['data-dat']
2021-12-30
Full example:
# import module
from bs4 import BeautifulSoup
# create data
dom = """<td class="select_date" data-dat="2021-12-30" data-dat-f="30. Dec 2021" data-global-index="32" data-title="30.12.2021" id="d30-12-2021"><span class="bubble">30</span></td>"""
soup = BeautifulSoup(dom, 'html.parser')
# Extract "data-dat" attribute
print(soup.find("td").attrs['data-dat'])
# 2021-12-30