Functions: Effectively/Logically hard coded max python version; exceeding results in silent failure and false pseudo-success

[paulpv]

I have Python 3.13 installed.

% python3.13 --version
Python 3.13.1

I am trying to follow the guide at https://firebase.google.com/docs/functions/get-started?gen=2nd and run firebase functions with:

firebase init functions
...
firebase emulators:start

The emulator says either...

Failed to load function definition from source: FirebaseError: Failed to find location of Firebase Functions SDK:
Missing virtual environment at venv directory. Did you forget to run 'python3.12 -m venv venv'?

... or, if I run cd ./functions && python3 -m venv venv...

Failed to load function definition from source: FirebaseError: Failed to find location of Firebase Functions SDK.
Did you forget to run '. "./functions/venv/bin/activate" && python3.12 -m pip install -r requirements.txt'?

I don't see that logged step documented anywhere.
Apparently you have to run the equivalent of:

pushd functions
python3 -m venv venv
source venv/bin/activate
pip install --upgrade pip
pip install -r requirements.txt
deactivate
popd
firebase emulators:start

But that is all moot because it still fails!

Looking at firebase-debug.log: EMPHASIS MINE

...
[info] i  functions: Watching "/Users/pv/Dev/GitHub/swooby/swoo.by/functions" for Cloud Functions... {"metadata":{"emulator":{"name":"functions"},"message":"Watching \"/Users/pv/Dev/GitHub/swooby/swoo.by/functions\" for Cloud Functions..."}}
[debug] [2025-03-18T21:38:02.543Z] Customer code is not Node
[debug] [2025-03-18T21:38:02.543Z] Validating python source
[debug] [2025-03-18T21:38:02.543Z] Building python source
[debug] [2025-03-18T21:38:02.543Z] Could not find functions.yaml. Must use http discovery
*****
[debug] [2025-03-18T21:38:02.545Z] Running command with virtualenv: command=., args=["\"/Users/pv/Dev/GitHub/swooby/swoo.by/functions/venv/bin/activate\"","&&","python3.12","-c","\"import firebase_functions; import os; print(os.path.dirname(firebase_functions.__file__))\""]
[debug] [2025-03-18T21:38:02.553Z] stderr: /bin/sh: python3.12: command not found
*****

[error] ⬢  functions: Failed to load function definition from source: FirebaseError: Failed to find location of Firebase Functions SDK. Did you forget to run '. "/Users/pv/Dev/GitHub/swooby/swoo.by/functions/venv/bin/activate" && python3.12 -m pip install -r requirements.txt'? {"metadata":{"emulator":{"name":"functions"},"message":"Failed to load function definition from source: FirebaseError: Failed to find location of Firebase Functions SDK. Did you forget to run '. \"/Users/pv/Dev/GitHub/swooby/swoo.by/functions/venv/bin/activate\" && python3.12 -m pip install -r requirements.txt'?"}}
[debug] [2025-03-18T21:38:02.555Z] Could not find VSCode notification endpoint: FetchError: request to http://localhost:40001/vscode/notify failed, reason: . If you are not running the Firebase Data Connect VSCode extension, this is expected and not an issue.
...

The root cause is that python3.12 is trying to be used.

Again, I have Python 3.13.

I tried setting firebase.json...

  "functions": [
    {
      "runtime": "python313",
...

...but firebase emulators:start fails with:

% firebase emulators:start
(node:78311) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
i  emulators: Starting emulators: functions, hosting, extensions
⚠  hosting: Port 6000 is restricted by some web browsers, including Chrome. You may want to choose a different port such as 6001.
i  emulators: Shutting down emulators.
i  hub: Stopping emulator hub

Error: Cannot load functions from ./functions because it has invalid runtime python313

Looking at https://github.com/firebase/firebase-tools/blob/master/src/deploy/functions/runtimes/python/index.ts

export function getPythonBinary(
  runtime: supported.Runtime & supported.RuntimeOf<"python">,
): string {
  if (process.platform === "win32") {
    // There is no easy way to get specific version of python executable in Windows.
    return "python.exe";
  }
  if (runtime === "python310") {
    return "python3.10";
  } else if (runtime === "python311") {
    return "python3.11";
  } else if (runtime === "python312") {
    return "python3.12";
  }
  assertExhaustive(runtime, `Unhandled python runtime ${runtime as string}`);
}

This code tells me that Python 3.13 (python313) released 2024-10-07 is not supported?!?!

Where is/are the required/supported python version numbers listed?

Why does specifying an existing valid "runtime": "python313" fail?

Why does defaulting to or specifying a not existing "runtime": "python312" not fail?

This is all a pretty big cluster F.

Wasn't this supposed to be fixed by #6866 ?

[REQUIRED] Environment info

firebase-tools: 13.34.0
Platform: macOS (I do not think this is macOS specific)

[REQUIRED] Test case

?

[REQUIRED] Steps to reproduce

1. Install Python 3.13 only (do not have any other Python 3 or 2 version installed).
2. Follow https://firebase.google.com/docs/functions/get-started?gen=2nd

firebase init functions

3. Init functions to use Python
4. VERY FRUSTRATINGLY, nothing in the documentation says that it seems like the following additional steps are required?:

pushd functions
python3 -m venv venv
source venv/bin/activate
pip install --upgrade pip
pip install -r requirements.txt
deactivate
popd

5. firebase emulators:start

[REQUIRED] Expected behavior

• firebase emulator functions work successfully

[REQUIRED] Actual behavior

• firebase emulator starts [false] successfully
• debug log says it failed to find python 3.12
• emulator functions page says

Failed to load function definition from source: FirebaseError: Failed to find location of Firebase Functions SDK. Did you forget to run '. "./functions/venv/bin/activate" && python3.12 -m pip install -r requirements.txt'?

WORKAROUND

Install Python 3.12, but that is a pretty sad/weak workaround.

[aalej]

Hey @paulpv, sorry to hear you encountered this issue, and thanks for sharing your observations as well as for creating a detailed report. I'll check this with our engineering team to see what we can do to improve this behavior and to add support for python3.13 runtime.

Regarding step 4, I think this occurred since python313 isn't yet listed in runtime versions. Usually, these steps(creating venv and installing dependencies) are handled by the Firebase CLI during initialization.

edit: At the moment, it doesn't look like the Python 3.13 runtime is supported in Cloud Run Functions https://cloud.google.com/static/functions/docs/concepts/execution-environment#python

[paulpv]

Thank you, @aalej .

I still find it odd that:

Why does defaulting to or specifying a not existing "runtime": "python312" not fail?

firebase emulators:start starts running and I would expect it to fail.

Understood about the supported versions lagging a little.

That same link shows Node is supported only up to v22, even though v23 released 2024/10/16.
But that is a major version that is even more understandable to take a little while to support.

Python 3.12->3.13 should be a pretty minor change that is relatively much easier to confirm support.