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?

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

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.