How to find elements without a specific attribute in BeautifulSoup?

Using Python and Beautifulsoup, to find elements without a specific attribute (like class) we can use find or find_all methods or CSS selectors:

import bs4
soup = bs4.BeautifulSoup("""
<a class="ignore">bad link</a>
<a>good link</a>
""")

soup.find_all("a", class_=None)
["<a>good link</a>]
# or using a lambda function:
soup.find_all("a", class_=lambda value: "ignore" not in value)
# or using regular expression
soup.find_all("a", class_=re.compile(""))