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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_instance( model, method="file", img_dir=None, data_dir=None, bucket=None ):
 """Return an instance of ConsumeStore."""

    global _instances
    if not isinstance(model, ConsumeModel):
        raise TypeError(
            "get_instance() expects a parker.ConsumeModel derivative."
        )

    if method == "file":
        my_store = store.get_filestore_instance(
            img_dir=img_dir,
            data_dir=data_dir
        )
    elif method == "s3":
        my_store = store.get_s3store_instance(
            bucket=bucket
        )
    else:
        raise ValueError("Unexpected method value, '%s'." % method)

    key = "%s:%s" % (repr(model), repr(my_store))

    try:
        instance = _instances[key]
    except KeyError:
        instance = ConsumeStore(model, my_store)
        _instances[key] = instance

    return instance