fixed

I agree. The largest obstacle in solving this was realising, that transaction_date was not actually a date, but a datetime/timestamp instead.

No, the description is in contradiction to the natural world where rooms don't have walls of 0 size and you don't calculate wallpaper rolls with w * l * h. :-)

Lifesaver.

Must use this approach more often.

Don't brute force then. Find a shortcut :)

Me too.

This should be voted best practice, as that's exactly what NumPy is for.

(defeated male leaves)

Thank you.

you're supposed to call the methods on an instance, not on the class

(the design of the task is completely bloated, actually, these should have been static or better, class methods. But definitely not instance methods)

TypeError: method() takes exactly 1 positional argument (2 given)

Explicitness is good for whoever is reading your code, but you've got to know how much explicitness is too much.

Elegant