优雅的方式来过滤无或不过滤

Question

The following SQLAlchemy code works, but looks un-pythonic:

if has_died: # has_died: True or False
  query = query.filter(User.died_at != None)
else:
  query = query.filter(User.died_at == None)

What is a more elegant way to add the filter?

Answer 1

Well, you could do this:

query = query.filter((User.died_at != None) if has_died else (User.died_at == None))

But it's a bit hard to read. I think how you're doing it is fine.

Answer 2

您可以使用三元运算符将其重写为一行

query = query.filter((User.died_at != None) if has_died else (User.died_at == None))

Answer 3

What about:

query = query.filter(bool(User.died_at) == has_died)

It returns:

• False if User.died_at is None and has_died is True
• True if User.died_at is None and has_died is False
• True if User.died_at is not None and has_died is True
• False if User.died_at is not None and has_died is False

Which is the intended behavior...

But then again, not sure if it is easier to understand than your piece of code!