A merged containers class

Definition

from itertools import chain
class merged (object):
    """
    Shadows multiple containers, treating them as one, performing
    iteration and membership testing over all of them in the order the
    class is instantiated with.
    """
    def __init__ (self, *args):
        self._containers = args
    def __len__ (self):
        return sum(len(c) for c in self._containers)
    def __iter__ (self):
        return chain(*self._containers)
    def __contains__ (self, item):
        for container in self._containers:
            if item in container:
                return True
        return False

Usage

letters = "a b c".split()
numbers = set((1, 2, 3))
both = merged(letters, numbers)
for item in both:
    print item,
# prints a b c 1 2 3
"a" in both # True
"e" in both # False
2 in both   # True
8 in both   # False