why use a main method 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: python main

if __name__ == "__main__":
    # execute only if run as a script
    main()