def __init__(self, iterable=None):
    self.end = end = []
    end += [None, end, end]
    self.map = {}
    if (iterable is not None):
        self |= iterable
def __init__(self, iterable=None):
    self.end = end = []
    end += [None, end, end]
    self.map = {}
    if (iterable is not None):
        self |= iterable