Repeatedly calling attr() on same attribute doesn't accumulate values about dominate HOT 1 OPEN

So technically your ideal/expected result is actually unexpected behavior. The documentation on the attr function literally says:

Set attributes on the current active tag context

So in essence what you're doing when you call attr(className = "bar") you're quite literally setting className (class) to "btn" then when you call it again with attr(className = "baz") it's literally setting className (class) to "baz".

What you'd really want is the addition of a function along the lines of append_attribute or something, which adds to a current attribute if it exists or falls back to just setting the attribute if it doesn't exist.

from dominate.