Question

I maintain a set that needs to be progressively shrunk, according to various conditions.

For example:

acceptable = read_input()
acceptable.rank_by_x()
acceptable = set(filter(is_rank_x_top_100, acceptable))
acceptable.rank_by_y()
acceptable = set(filter(is_rank_y_top_10, acceptable))

It works, but the set(filter()) construct looks ugly. Is there a better way to do that? Or is it better to just subclass set to add a method that does the same?

Answer 1

You may collapse this to:

acceptable = set()
#...
acceptable = set(filter(is_rank_y_top_10,
                        filter(is_rank_x_top_100, acceptable)))

Or use comprehensions:

acceptable = set()
#...
acceptable = set(i for i in acceptable
                 if is_rank_x_top_100(i) and is_rank_y_top_10(i))