Repacking structs to minimise bit wastage

repack.py

from queue import PriorityQueue

class Field:
    def __init__(self, size, align):
        self.size = size
        self.align = align

class Struct:
    def __init__(self, fields):
        size = 0
        waste = 0
        align = 1

        for field in fields:
            size += field.size

            while size % field.align != 0:
                size += 1
                waste += 1

            if field.align > align:
                align = field.align

        while size % align != 0:
            size += 1

        self.fields = fields
        self.size = size
        self.waste = waste

    def __lt__(self, other):
        return self.waste < other.waste

def repack(fields):
    fields = set(fields)

    queue = PriorityQueue()
    queue.put(Struct([]))

    while True:
        struct = queue.get()
        remaining = fields - set(struct.fields)

        if not remaining:
            return struct

        for field in remaining:
            queue.put(Struct(struct.fields + [field]))