TypeError: main() takes 0 positional arguments but 1 was given

import tensorflow as tf

def main():
    print('hello')
    
if __name__ == '__main__':
    tf.app.run()

会报错 TypeError: main() takes 0 positional arguments but 1 was given

def main(_)

这样就不会报错，_的用法和具体原因后续补上，目前还没弄明白，占位符？