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What does if name == "main": do?

What does this do, and why should one include the if statement?

if __name__ == "__main__":
    print("Hello, World!")

_{If you are trying to close a question where someone should be using this idiom and isn't, consider closing as a duplicate of Why is Python running my module when I import it, and how do I stop it? instead. For questions where someone simply hasn't called any functions, or incorrectly expects a function named main to be used as an entry point automatically, use Why doesn't the main() function run when I start a Python script? Where does the script start running?.}

Answer*

Every module in Python has an attribute called `__name__`. The value of `__name__`  attribute is  `__main__` when the module is run directly, like `python my_module.py`. Otherwise (like when you say `import my_module`) the value of `__name__`  is the name of the module.

Small example to explain in short.

### Script *test.py*

    apple = 42

    def hello_world():
        print("I am inside hello_world")

    if __name__ == "__main__":
        print("Value of __name__ is: ", __name__)
        print("Going to call hello_world")
        hello_world()

We can execute this directly as

```lang-none
python test.py
```

Output

```lang-none
Value of __name__ is: __main__
Going to call hello_world
I am inside hello_world
```

Now suppose we call the above script from another script:

### Script *external_calling.py*

    import test

    print(test.apple)
    test.hello_world()

    print(test.__name__)

When you execute this,

```lang-none
python external_calling.py
```

Output

```lang-none
42
I am inside hello_world
test
```

So, the above is self-explanatory that when you call *test* from another script, if loop `__name__` in `test.py` will not execute.

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What does if __name__ == "__main__": do?

Answer*

What does if name == "main": do?