Sort Python list of objects by date (when some are None)

Question

This is a slight update to my previous question

I have a Python list called results. Most result objects in the results list have a person object, and most person objects have a birthdate property (result.person.birthdate). The birthdate is a datetime object.

I would like to order the list of results by birthdate with the oldest first. However, if there isn't a person object or the person object doesn't have a birthdate I would still like the result included in the list of results. At the end of the list would be ideal.

What is the most Pythonic way to do this?

Answer 1

def birthdate_key(x):
  missing = (x.person is None or x.person.birthdate is None)
  return (missing, x.person.birthdate if not missing else None)

results.sort(key=birthdate_key)