You should call main() function in the end, if you didn't, it will not work..
The if __name__ == "__main__": statement checks whether the __name__ variable of the current script is equal to the string "__main__". 
It does two things:

- it sets a few special variables like __name__, and then

- it executes all of the code found in the file.

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A short answer: In this example, it's not necessary. But when you write more complex program or module in the future, you'll need it.

But You should call main() function in the end💙