py -3.x does not automatically install python

[Frame42]

Bug report

Bug description:

I'm trying to deploy the new python installer in the most backward compatible way. My experimentation is that calling py -3.11 does NOT trigger the automatic install as expected. However py exec -3.11 does work as intended.

C:\Users\me>py help
Python installation manager 25.0
[...]
C:\Users\me>py -3.11
[ERROR] No runtime installed that matches 3.11. Try running "py install 3.11".

C:\Users\me>py exec -3.11
********************************************************************************
Installing Python 3.11.9.
Extracting: ...................................................................✅
To see all available commands, run 'py help'
********************************************************************************
Python 3.11.9 (tags/v3.11.9:de54cf5, Apr  2 2024, 10:12:12) [MSC v.1938 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> 

Refering to the documentation, I was not expecting that difference:
https://docs.python.org/dev/using/windows.html#basic-use: "The only difference between the two commands is when running without any arguments: py will install and launch your default interpreter, while pymanager will display help (pymanager exec ... provides equivalent behaviour to py ...)."

https://docs.python.org/dev/using/windows.html#configuration
"True to allow automatic installs when specifying a particular runtime to launch. By default, true."

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[johnslavik]

Hello! @zooba would you take a look?

This is a pymanager issue -- we generally report these in https://github.com/python/pymanager.

[johnslavik]

CC @ZeroIntensity (mentorship): we could label this as OS-windows and topic-installation

[Frame42]

we generally report these in https://github.com/python/pymanager.

Sorry about that, I did not search for it long enough.

I followed the "our bug tracker" link in https://docs.python.org/3/using/windows.html#troubleshooting which leads here, even though it is from the "Python Install Manager" section

[zooba]

Yeah, I'll transfer it, but it's also going to be closed as won't fix. The requested behaviour was my original plan, but people insisted it be changed to be consistent with the previous launcher.

You can use the configuration to enable automatic installs, or always using py exec ... to get the automatic install behaviour.

[Frame42]

You can use the configuration to enable automatic installs, or always using py exec ... to get the automatic install behaviour.

I tried adding both the environment variable and the pymanager.json setting but was never able to get py -3.x command to install python.

C:\Users\me>set PYTHON_MANAGER_AUTOMATIC_INSTALL=true

C:\Users\me>py -3.11
[ERROR] No runtime installed that matches 3.11. Try running "py install 3.11".

[zooba]

I tried adding both the environment variable and the pymanager.json setting but was never able to get py -3.x command to install python.

Ah, you're right. It's there to disable autoinstall when using py exec, not to enable it when you aren't. I think we can probably change it to infer the default (which is based on argv[0] and argv[1]) rather than inferring an "and".

I'll reopen this to cover that change. Specifically, we're not changing the default behaviour of py -V:... - only the ability for the configuration to override that default behaviour.

[pfmoore]

The behaviour you're seeing is as defined in the PEP introducing the new manager:

If no matching runtime is found, the py exec and pymanager exec commands will automatically install and launch one (user configuration permitting). The py, python and python3 commands will report and error and exit.

So this is simply a documentation error - the docs don't explicitly mention that auto installation doesn't happen for the raw py -3.X command. If you want auto installation, use py exec -3.X.

❯ py -3.10
[ERROR] No runtime installed that matches 3.10. Try running "py install 3.10".
❯ py exec -3.10
********************************************************************************
Installing Python 3.10.11.
Downloading: ..................................................................✅
Extracting: ...................................................................✅
To see all available commands, run 'py help'
********************************************************************************
Python 3.10.11 (tags/v3.10.11:7d4cc5a, Apr  5 2023, 00:38:17) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> ^Z

[Frame42]

Summarizing the changes that I think should be made to the doc:

2 paragraphs of Basic use should be updated:

• "The only difference between the two commands is when running without any arguments: py will install and launch your default interpreter, while pymanager will display help (pymanager exec ... provides equivalent behaviour to py ...)."
  py will install only if you call py exec
• "When you launch either python or py but do not have any runtimes installed, and the requested version is the default, it will be installed automatically and then launched. Otherwise, the requested version will be installed if automatic installation is configured (most likely by setting PYTHON_MANAGER_AUTOMATIC_INSTALL to true), or if the py exec or pymanager exec forms of the command were used."

https://docs.python.org/3/using/windows.html#troubleshooting "our bug tracker" needs to point to the pymanager bug tracker instead of CPython.

and maybe you want to mention the automatic install mechanism in 4.1.5. Installing runtimes

Thanks for the quick replies !

[Frame42]

To clarify on the second bullet of my last post. The first sentence of that paragraph is true: if there are no runtimes installed at all, then py -3.x will install.

C:\Users\me>py uninstall 3.9
Uninstall Python 3.9.13? [Y/n]
Removed Python 3.9.13

C:\Users\me>py -0

C:\Users\me>py -3.11 --version
********************************************************************************
Installing Python 3.11.9.
Extracting: ...................................................................✅
To see all available commands, run 'py help'
********************************************************************************
Python 3.11.9

C:\Users\me>py -3.12 --version
[ERROR] No runtime installed that matches 3.12. Try running "py install 3.12".

The PEP text says it all.