def problems(pending, done):
    last = None
    if not pending:
        raise StopIteration()
    for migration in pending:
        if migration is done:
            last = migration
            continue
        if last and migration not in done:
            yield last, migration
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/South-1.0.2/south/migration/__init__.py/problems/operator `in` -> `is`