<filename>what_is_the_name_main_in_python/demo1.py
def a1_func():
    print('hello a1_func')


print('demo1.py is called')
a1_func()

<filename>what_is_the_name_main_in_python/demo1.py
def a1_func():
    print('hello a1_func')


print('demo1.py is called')
a1_func()
