Auto activate venv when python-version is set

.github/workflows/test.yml

@@ -143,17 +143,27 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.12", "3.13t"]
+        os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
       - uses: actions/checkout@v4
       - name: Install latest version
         uses: ./
         with:
-          python-version: ${{ matrix.python-version }}
+          python-version: 3.13.1t
       - name: Verify UV_PYTHON is set to correct version
         run: |
-          if [ "$UV_PYTHON" != "${{ matrix.python-version }}" ]; then
+          echo "$UV_PYTHON"
+          if [ "$UV_PYTHON" != "3.13.1t" ]; then
             exit 1
           fi
-      - run: uv sync
-        working-directory: __tests__/fixtures/uv-project
+        shell: bash
+      - name: Verify packages can be installed
+        run: uv pip install --python=3.13.1t pip
+        shell: bash
+      - name: Verify python version is correct
+        run: |
+          python --version
+          if [ "$(python --version)" != "Python 3.13.1" ]; then
+            exit 1
+          fi
+        shell: bash

README.md

@@ -72,15 +72,20 @@ to install the latest version that satisfies the range.
 
 ### Python version
 
-You can use the input `python-version` to set the environment variable `UV_PYTHON` for the rest
-of your workflow.
+You can use the input `python-version` to
+
+- set the environment variable `UV_PYTHON` for the rest of your workflow
+- create a new virtual environment with the specified python version
+- activate the virtual environment for the rest of your workflow
+
 This will override any python version specifications in `pyproject.toml` and `.python-version`
 
 ```yaml
-- name: Install the latest version of uv and set the python version to 3.12
+- name: Install the latest version of uv and set the python version to 3.13t
   uses: astral-sh/setup-uv@v4
   with:
-    python-version: "3.12"
+    python-version: 3.13t
+- run: uv pip install --python=3.13t pip
 ```
 
 You can combine this with a matrix to test multiple python versions:

action.yml

@@ -14,8 +14,7 @@ inputs:
     required: false
   github-token:
     description:
-      "Used to increase the rate limit when retrieving versions and downloading
-      uv."
+      "Used to increase the rate limit when retrieving versions and downloading uv."
     required: false
     default: ${{ github.token }}
   enable-cache:

src/setup-uv.ts

@@ -23,6 +23,7 @@ import {
   toolDir,
   version,
 } from "./utils/inputs";
+import * as exec from "@actions/exec";
 
 async function run(): Promise<void> {
   const platform = getPlatform();
@@ -46,7 +47,7 @@ async function run(): Promise<void> {
     addUvToPath(setupResult.uvDir);
     addToolBinToPath();
     setToolDir();
-    setupPython();
+    await setupPython();
     addMatchers();
     setCacheDir(cacheLocalPath);
 
@@ -125,10 +126,24 @@ function setToolDir(): void {
   }
 }
 
-function setupPython(): void {
+async function setupPython(): Promise<void> {
   if (pythonVersion !== "") {
     core.exportVariable("UV_PYTHON", pythonVersion);
     core.info(`Set UV_PYTHON to ${pythonVersion}`);
+    const options: exec.ExecOptions = {
+      silent: !core.isDebug(),
+    };
+    const execArgs = ["venv", "--python", pythonVersion];
+
+    core.info("Activating python venv...");
+    await exec.exec("uv", execArgs, options);
+
+    let venvBinPath = ".venv/bin";
+    if (process.platform === "win32") {
+      venvBinPath = ".venv/Scripts";
+    }
+    core.addPath(venvBinPath);
+    core.exportVariable("VIRTUAL_ENV", venvBinPath);
   }
 }