def __enter__(self):
    cls = type(self)
    self.__previous_instances.append(cls._contexts.current.get(cls.__name__, None))
    cls._contexts.current[cls.__name__] = self
insert num_columns columns at position.
dataset/ETHPy150Open viewfinderco/viewfinder/backend/base/context_local.py/ContextLocal.__enter__--crossover with--dataset/ETHPy150Open CGATOxford/cgat/CGAT/Mali.py/AlignedString.insertColumns