gh-120743: Soft deprecate os.popen() function

[vstinner]

Soft deprecate os.popen(), os.spawn*() and os.system() functions.

• Issue: Soft deprecate os.spawn*(), os.popen() and os.system() functions #120743

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📚 Documentation preview 📚: https://cpython-previews--120744.org.readthedocs.build/

[vstinner]

cc @gpshead

[zooba]

I don't like system being a deprecation. I have no concerns about recommending people use subprocess.run or equivalent if they're unsure, but there's no harm in os.system being used. If there were problems, we'd have heard reports of them by now.

[zooba]

Suggested change

	.. deprecated:: 3.14
	The function is :term:`soft deprecated` and should no longer be used to
	write new code. The :mod:`subprocess` module is recommended instead.

I don't like this one

[gpshead]

but there's no harm in os.system being used. If there were problems, we'd have heard reports of them by now.

Anything silently using a shell opens the world up for problems that are not obvious to many code authors. Shell injection, quoting hell, spaces, etc. It is fair to say that the world has heard so much about that over the decades that many of us don't even notice that screaming noise anymore.

this is just a soft deprecation in the docs to point people towards the well lit path of subprocess.run().

[zooba]

Anything silently using a shell opens the world up for problems that are not obvious to many code authors.

If you can recognise the implications of shell=True but not os.system, then I don't think there's anything we can do on our side short of removing both.

There isn't a case where they behave featurefully different, right? Like, os.system isn't going to choose not to create a shell in some cases?

[adorilson]

Is it time to add a new Superseded functions section to the Superseded page and put these functions there, or is this restricted to modules?

[vstinner]

I removed os.system() deprecation. We can revisit its deprecation once subprocess.shell() will be added or not: #121093

I kept the non-controversial deprecations.

[vstinner]

Is it time to add a new Superseded functions section to the Superseded page and put these functions there, or is this restricted to modules?

It seems like a huge maintenance burden to maintain such hypothetical (long) list in the documentation. I don't think that it's worth it, but you can open an issue if you disagree and consider that it's a good idea :-)