if __name__ == '__main__':
    print('script_2 is the main!')

import importlib.util
spec = importlib.util.spec_from_file_location('__main__', 'script_2.py')
mod = importlib.util.module_from_spec(spec)
spec.loader.exec_module(mod)
if __name__ == '__main__':
    print('script_3 is the main!')

python script_1.py
> script_2 is the main!
> script_1 is the main!