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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 all_entity_classes():
 """Return the list of all concrete persistent classes that are subclasses of Entity."""

    persistent_classes = Entity._decl_class_registry.values()
    # with sqlalchemy 0.8 _decl_class_registry holds object that are not
    # classes
    return [
        cls for cls in persistent_classes if isclass(cls) and issubclass(cls, Entity)
    ]