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## Mac/Linux

In this environment, Python scripts can be given a [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)) line that tells the operating system that the file is a script, and what interpreter (i.e., Python) to use for it. Because `#` starts a comment in Python, Python itself doesn't need any special handling for this - it's just ignored anyway. Of course, the file also needs to be marked as executable (`chmod +x`).

Keep in mind that without a shebang, the operating system will typically try to treat the script as a *shell* script, which will fail completely (probably with many errors). The operating system doesn't care about a `.py` extension on the file name - only the shebang matters.

It's common to use something like `#!/usr/bin/env python`, to allow the operating system to find Python. But sometimes it's necessary to give the path to a specific Python to make the script work properly.

It's also common for such scripts to name the file *without* a `.py` extension (so just `myscript`), and to *not* use a `if __name__ == '__main__':` guard. That's because a script like this will normally *only* be used as a script and *should not* ever be `import`ed from somewhere else - so it's completely unnecessary and inelegant to add those things.

<details><summary>Complete example</summary>

How the script is named, and the permissions:
```lang-none
$ ls
myscript
$ stat -c '%A' myscript 
-rwxrwxr-x
```
What's in it:
```python
$ cat myscript 
#!/usr/bin/env python

def my_function():
    print("Test")

my_function()
```
How we run it, and what happens:
```lang-none
$ ./myscript 
Test
```
</details>

## Windows

Windows doesn't care about shebangs generally, and doesn't have a concept of executable text files. However, it does have a concept of file associations - so we can tell Windows to use Python (via a specific path to `python`, perhaps something like<br>`C:\Program Files\Python 3.12\python.exe`) to open any file with a `.py` file name extension when it's double-clicked.

But better yet, we can tell it to use [the Python Launcher for Windows](https://docs.python.org/3/using/windows.html#python-launcher-for-windows). There's only one of these even if you install multiple versions of Python, and it's in a single, consistent place -<br>`C:\Windows\py.exe` (assuming Python was installed "for all users"). More importantly, this `py` program *tries to read and understand shebang lines* - simply write the script *as if* it would run on a Mac or Linux system, and let `py` do the rest.
</details>