def flatten(iterable):
    return (x for e in iterable for x in e)
Create a L{ShadowDatabase} with no user data in it.
dataset/ETHPy150Open OP2/PyOP2/pyop2/utils.py/flatten--crossover with--dataset/ETHPy150Open nlloyd/SubliminalCollaborator/libs/twisted/python/test/test_fakepwd.py/ShadowDatabaseTests.setUp