from collections import MutableSet

class WithSet(MutableSet):
    
    def __init__(self, it=()):
        self.data = set(it)

    def __len__(self):
        return len(self.data)

    def __iter__(self):
        return iter(self.data)

    def __contains__(self, item):
        return item in self.data

    def add(self, item):
        self.data.add(item)

    def discard(self, item):
        self.data.discard(item)

class WithList(MutableSet):

    def __init__(self, it=()):
        self.data = list(it)

    def __len__(self):
        return len(self.data)

    def __iter__(self):
        return iter(self.data)

    def __contains__(self, item):
        return item in self.data

    def add(self, item):
        if item not in self.data:
            self.data.add(item)

    def discard(self, item):
        try:
            self.data.remove(item)
        except ValueError:
            pass