feat(python): auto-activate venv before hook execution by mwbrooks · Pull Request #347 · slackapi/slack-cli

mwbrooks · 2026-02-21T01:26:07Z

Changelog

When running Slack CLI commands in a Bolt Python project, the CLI will attempt to automatically activate the venv. This will allow commands that use the slack-cli-hooks Python package to safely and successfully run even when the terminal system doesn't have the virtual environment activated.

Summary

This pull request gives Python the "create and run" experience that Node and Deno enjoy.

It enables auto-activation of venv, when it exists, so that commands can run safely and successfully even when the terminal session doesn't have a virtual environment activated. When the .venv is missing, the CLI will continue like normal.

Test coverage:

I noticed that the test coverage is reported as being low
Checking locally, it should be higher than reported
I'm hopeful that once mwbrooks-python-venv is merged, this branch will report higher coverage

Merge order:

This PR depends on the branch mwbrooks-python-venv
First merge mwbrooks-python-venv then merge this PR into main

Preview

2026-02-20-create-run-python.mov

Reviewers

Bolt for Python:

$ lack create my-test-app/
# → Select "AI Agent App"
# → Select "Bolt for Python"

# Validate output:
# → Confirm: "Created virtual environment at .venv"
# → Confirm: "Installed dependencies from pyproject.toml"
# → Confirm: "Installed dependencies from requirements.txt"
# → Confirm: No errors

# Run the app
$ cd my-test-app/
$ lack run
# → Confirm: App starts

# Clean up
$ cd ../
$ rm -rf my-test-app/

Bolt for JavaScript:

$ lack create my-test-app/
# → Select "AI Agent App"
# → Select "Bolt for JavaScript" <---- Not Python

# Validate output:
# → Confirm: No errors

# Run the app
$ cd my-test-app/
$ lack run
# → Confirm: App starts

# Clean up
$ cd ../
$ rm -rf my-test-app/

Requirements

I've read and understood the Contributing Guidelines and have done my best effort to follow them.
I've read and agree to the Code of Conduct.

Swap pip install order so pyproject.toml is installed first to set up the project package, then requirements.txt pins take precedence as the lockfile.

…for pip

Set VIRTUAL_ENV, prepend venv bin to PATH, and unset PYTHONHOME on the CLI process before any hooks run. This lets hook scripts (e.g. get-hooks, start, deploy) resolve the venv's Python and installed packages without requiring developers to manually activate the venv. Activation happens in InitSDKConfig after finding the project root and before reading/executing hooks. It is a no-op when no .venv exists, so non-Python projects are unaffected. Failure is non-fatal (debug log).

Clarify error messages in installPyProjectToml to include "updating pyproject.toml" context, and remove early return on file update errors so pip install is attempted regardless.

Route createVirtualEnvironment and runPipInstall through HookExecutor instead of os/exec, matching the npm runtime pattern. This makes the functions testable with the mock filesystem. Also add missing AddDefaultMocks call, remove stale test cases, and fix assertion strings.

Return a boolean from ActivateVenvIfPresent to indicate whether activation occurred, and log a debug message on success.

codecov · 2026-02-21T01:28:56Z

Codecov Report

❌ Patch coverage is 41.66667% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.67%. Comparing base (3417188) to head (8554adc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/runtime/python/python.go	50.00%	4 Missing and 4 partials ⚠️
internal/shared/clients.go	0.00%	2 Missing and 2 partials ⚠️
internal/slackdeps/os.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #347   +/-   ##
=======================================
  Coverage   64.66%   64.67%           
=======================================
  Files         213      213           
  Lines       18018    18042   +24     
=======================================
+ Hits        11652    11668   +16     
- Misses       5277     5282    +5     
- Partials     1089     1092    +3

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

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mwbrooks

Comments for those kind reviewers! 🙇🏻

mwbrooks · 2026-02-21T01:27:36Z

internal/runtime/python/python.go

+	if err := os.Setenv("VIRTUAL_ENV", venvPath); err != nil {
+		return false, err
+	}
+	if err := os.Setenv("PATH", binDir+string(filepath.ListSeparator)+os.Getenv("PATH")); err != nil {
+		return false, err
+	}
+	os.Unsetenv("PYTHONHOME")


note: I imagine we should create wrappers for these calls in our slackdeps.Os 🤔

note: I updated this PR to use slackdeps.Os and added slackdeps.Os.lookupEnv.

@mwbrooks 🌲 So good! I think we'll want to reuse this in other places soon?

mwbrooks · 2026-02-21T01:29:24Z

internal/runtime/runtime.go

+// ActivatePythonVenvIfPresent activates a Python virtual environment if one
+// exists in the given project directory. This sets VIRTUAL_ENV, prepends the
+// venv bin directory to PATH, and unsets PYTHONHOME on the current process so
+// that child processes (hook scripts) inherit the activated venv.
+func ActivatePythonVenvIfPresent(fs afero.Fs, projectDir string) (bool, error) {
+	return python.ActivateVenvIfPresent(fs, projectDir)
+}
+


note: While it feels wrong to have Python in the generic runtime this allows us to activate it for any project. We could move this into the Python runtime and think of a more general function that could be used across all runtimes.

Upside of this approach is that JS projects that include a .venv (perhaps for scripts) can be activated automatically.

mwbrooks · 2026-02-21T01:30:10Z

internal/shared/clients.go

+	if activated, err := runtime.ActivatePythonVenvIfPresent(c.Fs, dirPath); err != nil {
+		c.IO.PrintDebug(ctx, "failed to activate Python virtual environment: %s", err)
+	} else if activated {
+		c.IO.PrintDebug(ctx, "Activated Python virtual environment .venv")


note: I'd love to display this in the regular output, but it's tough to get a nice format because it can be displayed in many different situations.

⚠️ suggestion(non-blocking): Your approach is solid, but we might consider outputting the errors as a warning while keeping expected activations to the debug logs?

Would love to hear your thoughts on this! IIRC logic similar to what's here exists for the get-hooks activation, but we often miss problems that should be at least reported. Even if the command continues I think!

…bility Add Unsetenv to the Os interface/implementation/mock and refactor ActivateVenvIfPresent to accept types.Os instead of calling the os package directly. This allows the test to use mocks instead of mutating the real process environment.

Adopt map-based table-driven test pattern from main while preserving new ActivateVenvIfPresent and getVenvBinDir functions and their tests. Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

zimeg

@mwbrooks This feels awesome to use! The steps after create are much more quick now and apps feel "lighter" to run somehow... 🐍

I'm merging this after leaving a few comments that weren't blocking but might be nice to follow up on as we encounter edges in approach - thanks for bringing this to the finish 🏁 ✨

zimeg · 2026-02-27T04:09:14Z

internal/runtime/python/python.go

+// getVenvBinDir returns the platform-specific bin directory inside a virtual environment
+func getVenvBinDir(venvPath string) string {
+	if runtime.GOOS == "windows" {
+		return filepath.Join(venvPath, "Scripts")
+	}
+	return filepath.Join(venvPath, "bin")
+}


👁️‍🗨️ issue(non-blocking): I'm finding the windows option is erroring with perhaps unrelated hook errors in execution explored in slackapi/python-slack-hooks#96

zimeg · 2026-02-27T04:17:26Z

internal/runtime/python/python.go

+	if !venvExists(fs, venvPath) {
+		return false, nil
+	}


🐍 question: Do we want to avoid reactivating a virtual environment if one is present? This might be an issue if different environments are activated for different reasons, but I'm unsure if that's a common practice.

I'm alright merging this without a clear answer to extend these approaches based on feedback! The happy path works so well and .venv appears to be convention without suggesting .venv.testing or similar.

zimeg · 2026-02-27T04:25:15Z

internal/shared/clients.go

+	if activated, err := runtime.ActivatePythonVenvIfPresent(c.Fs, dirPath); err != nil {
+		c.IO.PrintDebug(ctx, "failed to activate Python virtual environment: %s", err)
+	} else if activated {
+		c.IO.PrintDebug(ctx, "Activated Python virtual environment .venv")


⚠️ suggestion(non-blocking): Your approach is solid, but we might consider outputting the errors as a warning while keeping expected activations to the debug logs?

Would love to hear your thoughts on this! IIRC logic similar to what's here exists for the get-hooks activation, but we often miss problems that should be at least reported. Even if the command continues I think!

mwbrooks added 15 commits February 20, 2026 10:24

feat(python): add support for creating and activating venv

9d6e1d9

fix(python): install pyproject.toml before requirements.txt

665e23c

Swap pip install order so pyproject.toml is installed first to set up the project package, then requirements.txt pins take precedence as the lockfile.

chore(cmd): remove venv detail from init command description

9008d02

fix(python): use correct python executable on Windows for venv creation

51030ee

chore(python): add comment explaining venv activation is unnecessary …

6e6ba42

…for pip

chore(python): fix gofmt formatting in python_test.go

cf35c5c

chore(python): move venv creation message to debug output

bff1d8c

chore(python): move dependency install messages to debug output

b0f0050

chore(python): shorten install success messages and highlight filenames

e641b20

fix(python): improve error handling for dependency file updates

4324103

Clarify error messages in installPyProjectToml to include "updating pyproject.toml" context, and remove early return on file update errors so pip install is attempted regardless.

test: remove skipped test

3a76ba8

Merge branch 'mwbrooks-python-venv' into mwbrooks-python-venv-activation

253ee65

feat(python): log debug message when venv is activated

adbda1b

Return a boolean from ActivateVenvIfPresent to indicate whether activation occurred, and log a debug message on success.

mwbrooks added this to the Next Release milestone Feb 21, 2026

mwbrooks self-assigned this Feb 21, 2026

mwbrooks added enhancement M-T: A feature request for new functionality changelog Use on updates to be included in the release notes semver:minor Use on pull requests to describe the release version increment area:bolt-python Related to github.com/slackapi/bolt-python labels Feb 21, 2026

mwbrooks commented Feb 21, 2026

View reviewed changes

mwbrooks added 4 commits February 20, 2026 18:40

test: add tests for ActivatePythonVenvIfPresent in runtime package

b75edb9

test: remove test comment

ce15297

fix: merge variable declaration with assignment to satisfy linter

f8755c9

mwbrooks marked this pull request as ready for review February 21, 2026 03:06

mwbrooks requested a review from a team as a code owner February 21, 2026 03:06

zimeg mentioned this pull request Feb 27, 2026

feat(python): add support for creating python .venv and installing dependencies #346

Merged

2 tasks

Base automatically changed from mwbrooks-python-venv to main February 27, 2026 02:58

chore: merge w main

8554adc

Adopt map-based table-driven test pattern from main while preserving new ActivateVenvIfPresent and getVenvBinDir functions and their tests. Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

zimeg approved these changes Feb 27, 2026

View reviewed changes

zimeg merged commit 4f51fa6 into main Feb 27, 2026
8 checks passed

zimeg deleted the mwbrooks-python-venv-activation branch February 27, 2026 04:27

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feat(python): auto-activate venv before hook execution#347

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