def event_callback(key):
    def decorator(func):
        func.event_key = key
        return func
    return decorator
Return all defined category names with at least one topic in
dataset/ETHPy150Open ARMmbed/htrun/mbed_host_tests/host_tests/base_host_test.py/event_callback--crossover with--dataset/ETHPy150Open evennia/evennia/evennia/help/manager.py/HelpEntryManager.get_all_categories