How to indent Python list-comprehensions?

Question

List comprehensions can be useful in certain situations, but they can also be rather horrible to read.. As a slightly exaggerated example, how would you indent the following?

Answer 1

It depends on how long they are. I tend to structure them like so:

[x.id for x
 in self.db.query(schema.allPostsUuid).execute(timeout=20)
 if x.type == 'post' 
    and x.deleted is not False
    and ...
    and ...]

That way every expression has its own line.

If any line becomes too big I like to extract it out in a lambda or expression:

transform = lambda x: x.id
results = self.db.query(schema.allPostsUuid).execute(timeout=20)
condition = lambda x: x.deleted is not False and ... and ...
[transform(x) for x in results if condition(x)]

And then if a lambda becomes too long it gets promoted to a function.