python: if no python, install uv and maybe create venv by isabelizimm · Pull Request #12904 · posit-dev/positron

isabelizimm · 2026-04-08T20:46:26Z

New registerRuntimePickerContribution API allowing extensions to add custom items to the interpreter picker
Full installation flow: install uv if needed -> select Python version -> install Python -> optionally create workspace venv
Option automatically hidden once a non-system Python is available

Release Notes

New Features

Provide support for installing uv #8359 If no usable Pythons are found, provide installation of uv and supported Python version.

Bug Fixes

N/A

QA Notes

@:win @:web

Be brave! Uninstall all non-System Pythons. For uv, it looks like this

uv cache clean
rm -r "$(uv python dir)"
rm -r "$(uv tool dir)"
rm ~/.local/bin/uv ~/.local/bin/uvx

Go to the Select Interpreter dropdown. You should see an option to install Python with uv.
Select the option to install Python with uv. The quickpick should show ONLY supported Python versions (3.9-3.14), in the MAJOR.MINOR format
Choose your Python version. This should install uv and then the chosen Python.
If you are in a workspace, next, you have the option to create a venv. If you are not in a workspace, you should not be asked if you want to make a venv since we won't know where to place it.
If creating a venv, it should be created and automatically selected in the Console.
In venv/non-venv case, you should see your new Python (and maybe your new venv) in the interpreter dropdown.
Once you have this new Python, you should no longer see the option to install Python in the interpreter dropdown

For automated testing purposes, we can force the "Install Python" option to always be shown in the "Select Interpreter" dropdown with the setting python.INTERNAL_alwaysShowUvInstallOption equal to True.

github-actions · 2026-04-08T20:46:49Z

E2E Tests 🚀
This PR will run tests tagged with: @:critical @:win @:web

^readme ^{valid tags}

rodrigosf672 · 2026-04-09T18:27:07Z

Thank you for the QA Notes, @isabelizimm. Creating an issue for automated testing for similar process to which you have outlined in the notes. cc @midleman @testlabauto

QA Notes

@:win @:web

Be brave! Uninstall all non-System Pythons. For uv, it looks like this
uv cache clean
rm -r "$(uv python dir)"
rm -r "$(uv tool dir)"
rm ~/.local/bin/uv ~/.local/bin/uvx  
Go to the Select Interpreter dropdown. You should see an option to install Python with uv.

Select the option to install Python with uv. The quickpick should show ONLY supported Python versions (3.9-3.14), in the MAJOR.MINOR format

Choose your Python version. This should install uv and then the chosen Python.

If you are in a workspace, next, you have the option to create a venv. If you are not in a workspace, you should not be asked if you want to make a venv since we won't know where to place it.

If creating a venv, it should be created and automatically selected in the Console.

In venv/non-venv case, you should see your new Python (and maybe your new venv) in the interpreter dropdown.

Once you have this new Python, you should no longer see the option to install Python in the interpreter dropdown

For automated testing purposes, we can force the "Install Python" option to always be shown in the "Select Interpreter" dropdown with the setting python.INTERNAL_alwaysShowUvInstallOption equal to True.

Copilot

Pull request overview

Adds a “Install Python via uv” path to Positron’s interpreter selection flow so users can bootstrap a supported Python install (and optionally a workspace venv) when no suitable Python is available.

Changes:

Adds a special quick pick entry in the runtime selector to trigger Python installation via uv.
Introduces a uvPythonInstaller helper to list supported Python versions from uv, install uv if needed, install a selected Python, and optionally create a venv in a workspace.
Updates the Python runtime manager/commands to support refresh + returning a selected runtime id, and adds unit tests for parsing/version filtering.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/vs/workbench/contrib/languageRuntime/browser/languageRuntimeActions.ts	Adds a quick pick option to install Python via `uv` and then select the newly installed runtime.
extensions/positron-python/src/client/pythonEnvironments/common/environmentManagers/uvPythonInstaller.ts	New implementation for listing/installing Python via `uv` and optionally creating a venv.
extensions/positron-python/src/client/pythonEnvironments/creation/createEnvApi.ts	Registers the `python.installPythonViaUv` command and returns the installed runtime info to the caller.
extensions/positron-python/src/client/common/constants.ts	Adds the `python.installPythonViaUv` command id constant.
extensions/positron-python/src/client/positron/manager.ts	Updates runtime selection to return a runtime id and adds an interpreter refresh helper.
extensions/positron-python/src/client/pythonEnvironments/common/environmentManagers/uv.ts	Exports shared regex/helpers used by the new installer.
extensions/positron-python/src/client/pythonEnvironments/creation/provider/uvCreationProvider.ts	Exports `createUvVenv()` for reuse in the install flow.
extensions/positron-python/src/test/pythonEnvironments/common/environmentManagers/uvPythonInstaller.unit.test.ts	Adds unit coverage for `uv python list` parsing/filtering/deduping/sorting behavior.
extensions/positron-python/src/test/configuration/interpreterSelector/commands/setInterpreter.unit.test.ts	Adjusts mocks for updated return type from `selectLanguageRuntimeFromPath()`.

isabelizimm · 2026-04-13T16:25:33Z

-			canPickMany: false
+	// Check if we should show the "Install Python via uv" option
+	// Only check after discovery is complete to avoid showing the option prematurely
+	const allowPythonInstall = configurationService.getValue<boolean>('python.allowPythonInstall') ?? true;


This is a command that folks can turn off if they don't want to be prompted to install uv. Right now this is the R person escape hatch, but I do worry it's heavy-handed.

isabelizimm · 2026-04-13T19:50:25Z

Okay, after chatting IRL we think it makes sense to make infra to allow languages to install themselves. Please hold on a review!

…andling - Fix $unregisterRuntimePickerContribution to actually dispose the contribution by tracking disposables in a Map keyed by handle - Extract duplicated installPythonViaUv result handling into shared helper - Fetch picker contribution items in parallel using Promise.all() - Add warning message when venv creation fails (falls back to base Python) - Add security note to installUv documenting the official installation pattern Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

isabelizimm · 2026-04-14T23:52:24Z

alright, i think this is ready again!

austin3dickey

Awesome work, this will be so nice! Haven't tested this yet but here are some code review thoughts.

austin3dickey · 2026-04-15T15:27:20Z

+        // Try to register the runtime
+        let metadata = await this.registerLanguageRuntimeFromPath(pythonPath, recreateRuntime);
+
+        // If registration failed, the interpreter might be newly created - trigger a refresh and retry


Interesting - I wonder if this will help with one of the new-PET problems detailed in #12116 or #12327!

austin3dickey · 2026-04-15T15:32:26Z

+ * Filters out pre-release versions and returns stable versions only.
+ * @returns Array of available Python versions, sorted by version descending
+ */
+export async function getAvailablePythonVersions(): Promise<UvAvailablePython[]> {


I think we have a lot of duplicate-ish code in uv.ts, uvCreationProvider.ts, and uvUtils.ts for dealing with python versions and installing python. Maybe you can reuse all or parts of those functions?

E.g. I'd think we'd want to use approximately the same code path if you're creating a new venv with the New Folder From Template flow vs. using the Python: Create Environment command vs. clicking the button in the interpreter picker. Though I get that might be tricker than I think it is, especially because I think there's some hardcoded python stuff in the core new folder service too.

austin3dickey · 2026-04-15T16:43:57Z

+
+    try {
+        // Use exec directly instead of installUvPython to avoid cache issues
+        // when uv was just installed in the same session


Hm, these caching issues might need a bit more love. Everything is working fantastically along the happy path making a venv inside a workspace. But when I do the flow outside a workspace,

the new interpreter that starts up is labeled Unknown, not uv

if I restart Positron it's not able to find that unknown interpreter and so it gives a scary "unable to start up; failed to resolve" error

I am wondering if both those issues would be solved if we somehow force Positron to re-check whether uv is installed? There's some caching on the UvUtils class that maybe we could invalidate upon successfully installing uv? Then theoretically if we refresh discovery it'll know the new interpreter is uv and maybe if the metadata lines up we won't see problem 2.

I also think there's a "python: clear cache and reload window" command, maybe we could hook into the cache-clear part of that?

I tried the flow again with uv already installed, and didn't see these problems. So I bet the "is uv installed" cache invalidation would solve them.

Ah, yeah we didn't have good a no-workspace fallback. I updated it to make a venv at $HOME/.venv . Do you think that's too heavy handed? I debated adding it to the ~/.positron dir, but that isn't as straightforward for discovery and the cwd for the console is $HOME too

austin3dickey · 2026-04-15T16:44:53Z

+                    return [
+                        {
+                            id: 'install-python-uv',
+                            label: '$(add) Install Python via uv',


Is it possible to use the lil Python icon instead of ➕ ? If that's too hard it's cool

austin3dickey · 2026-04-15T17:17:28Z

+
+    try {
+        if (process.platform === 'win32') {
+            await exec('powershell', [


I tested on Windows ARM, and everything generally worked, though it ended up installing an x64 python instead of arm64. So I got the warning popup that there was an architecture mismatch. Python was still able to run though I'd guess that certain compiled libraries wouldn't work.

I found this:

uv installs x86_64 Python on arm64 Windows astral-sh/uv#12906

which has the comment

I believe you can set UV_PYTHON=arm64.

Maybe we should detect the arch and set that?

Looks like uv python list needs the --all-arches flag too.

Co-authored-by: Austin Dickey <austin3spammy@gmail.com> Signed-off-by: Isabel Zimmerman <54685329+isabelizimm@users.noreply.github.com>

austin3dickey

Awesome, looks great and Mac works well for me! I still want to test on Windows and Web before approving if that's okay. Else you can merge.

austin3dickey · 2026-04-21T16:07:35Z

+            return pythonPath;
+        }
+
+        traceError('Could not find installed Python path');


Cool, everything is working on web!

On ARM Windows, I see this:

2026-04-21 10:50:44.507 [info] > uv python list --all-arches 2026-04-21 10:50:46.377 [info] Installing Python 3.14 via uv... 2026-04-21 10:50:46.392 [info] > uv python install --python-platform windows-arm64 3.14 2026-04-21 10:50:46.433 [info] Python 3.14 installed successfully 2026-04-21 10:50:46.440 [info] > uv python find 3.14 2026-04-21 10:50:46.746 [error] Could not find installed Python path

and it's not able to proceed.

I think it's because --python-platform isn't a thing:

PS C:\Users\austin> uv python install --python-platform windows-arm64 3.14 error: unexpected argument '--python-platform' found tip: a similar argument exists: '--python-fetch' Usage: uv.exe python install [OPTIONS] [TARGETS]... For more information, try '--help'.

So a couple things:

Not sure why the logs say it was installed successfully

I looked into it some more and the only way I could get it to work was doing uv python install cpython-3.14.4-windows-aarch64-none (that is, supply the full name including arch). Using an arg or an env var wasn't helping.

is cpython-3.14.4-windows-aarch64-none the output when you run uv python list? Trying to figure out how to snag that identifier without generating it ourselves 👀

Yes that's the identifier! (The first column in uv python list --all-arches)

isabelizimm · 2026-04-21T21:27:09Z

+        const installTarget = identifier ?? version;
+        await exec('uv', ['python', 'install', installTarget], { throwOnStdErr: false });


okay, here's what is happening for Windows now! We only pass the identifier on Windows ARM builds, so it will be picked up for that platform but otherwise just use the vanilla version

austin3dickey

Everything works perfectly! Thanks for all your work on this, this is huge!

install uv and create venv

3e8193b

rodrigosf672 mentioned this pull request Apr 9, 2026

automated testing for quick, low-friction python uv installation #12931

Open

wait for interpreter discovery to finish

5b4f364

isabelizimm requested a review from Copilot April 13, 2026 15:17

Copilot started reviewing on behalf of isabelizimm April 13, 2026 15:18 View session

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add tests

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isabelizimm commented Apr 13, 2026

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updates from review

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isabelizimm marked this pull request as ready for review April 13, 2026 18:35

isabelizimm requested a review from austin3dickey April 13, 2026 18:35

isabelizimm and others added 4 commits April 14, 2026 06:08

create arbitrary item in quickpick

6540eab

skip tests if api not available

3e06822

rearrange tests

b78059d

austin3dickey reviewed Apr 15, 2026

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isabelizimm and others added 4 commits April 15, 2026 18:09

Apply suggestions from code review

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Co-authored-by: Austin Dickey <austin3spammy@gmail.com> Signed-off-by: Isabel Zimmerman <54685329+isabelizimm@users.noreply.github.com>

first pass of fixes from review

39b5dbf

no workspace venvs go to home

4f6af70

lint

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isabelizimm requested a review from austin3dickey April 17, 2026 19:30

austin3dickey reviewed Apr 17, 2026

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Comment thread ...ositron-python/src/client/pythonEnvironments/common/environmentManagers/uvPythonInstaller.ts

isabelizimm mentioned this pull request Apr 21, 2026

update Python discovery docs to include uv installation #13103

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isabelizimm mentioned this pull request Apr 21, 2026

Allow uv installation from the new project flow #13104

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austin3dickey reviewed Apr 21, 2026

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isabelizimm added 3 commits April 21, 2026 14:51

use identifier

15f6a14

use identifier ONLY for windows

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update comment

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isabelizimm commented Apr 21, 2026

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isabelizimm requested a review from austin3dickey April 21, 2026 21:28

austin3dickey approved these changes Apr 22, 2026

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isabelizimm merged commit 8d93e51 into main Apr 22, 2026
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isabelizimm deleted the iz/download-uv branch April 22, 2026 14:14

github-actions Bot locked and limited conversation to collaborators Apr 22, 2026

		const installTarget = identifier ?? version;
		await exec('uv', ['python', 'install', installTarget], { throwOnStdErr: false });

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isabelizimm commented Apr 8, 2026 •

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