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.

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).

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 64.70%. Comparing base (180d499) to head (f8755c9).

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                    @@
##           mwbrooks-python-venv     #347      +/-   ##
========================================================
- Coverage                 64.77%   64.70%   -0.08%     
========================================================
  Files                       212      212              
  Lines                     17860    17884      +24     
========================================================
+ Hits                      11569    11571       +2     
- Misses                     5212     5224      +12     
- Partials                   1079     1089      +10

☔ 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 · 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.

…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.

mwbrooks added 3 commits February 20, 2026 13:53

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

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

feat(python): auto-activate venv before hook execution#347
mwbrooks wants to merge 7 commits intomwbrooks-python-venvfrom
mwbrooks-python-venv-activation

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mwbrooks commented Feb 21, 2026 •

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