is it necessary to declare a main function in python code example

Example 1: how to define main in python

# Defining main function 
def main(): 
    print("hello World") 
  
  
# Using the special variable  
# __name__ 
if __name__=="__main__": 
    main()

Example 2: main function python\

print("Hello")

print("__name__ value: ", __name__)


def main():
    print("python main function")


if __name__ == '__main__':
    main()