Q:

How to indent Python list-comprehensions?

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]

A:

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.

A:

Where I work, our coding guidelines would have us do something like this:
all_posts_uuid_query = self.db.query(schema.allPostsUuid)
all_posts_uuid_list = all_posts_uuid_query.execute(timeout=20)
all_uuid_list = [
    x.id 
    for x in all_posts_uuid_list 
    if (
        x.type == "post" 
        and 
        not x.deleted  # <-- if you don't care about NULLs / None
    )
]

A:

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

