def __init__(self, b_val):
    assert b_val is not None, "Cannot wrap None"
    assert not isinstance(b_val, list), repr(b_val)
    self.b_val = b_val
Constructor.  Argument is the base value to be wrapped.
dataset/ETHPy150Open GoogleCloudPlatform/datastore-ndb-python/ndb/model.py/_BaseValue.__init__