def combine(default, extra):
    """
    Take two dicts and create a third dict with all the keys
    from both.  If both dicts share a key, the second dict
    overrides the first.  Return the new dict.
    """
    new = {}
    for key, value in default.items():
        new[key] = value
    for key, value in extra.items():
        new[key] = value
    return new
