feat: do not create __pycache__ in lib dir (#1469)

**Issue number:**
[ADDON-76503](https://splunk.atlassian.net/browse/ADDON-76503)

### PR Type

**What kind of change does this PR introduce?**
* [x] Feature
* [ ] Bug Fix
* [ ] Refactoring (no functional or API changes)
* [ ] Documentation Update
* [ ] Maintenance (dependency updates, CI, etc.)

## Summary

### Changes

Compiled Python files are created when UCC checks using pip whether a
library is installed.

This prevents it from doing that.

### User experience

Output directory with lib dir that does not contain `__pycache__`.

## Checklist

If an item doesn't apply to your changes, leave it unchecked.

* [x] I have performed a self-review of this change according to the
[development
guidelines](https://splunk.github.io/addonfactory-ucc-generator/contributing/#development-guidelines)
* [x] Tests have been added/modified to cover the changes [(testing
doc)](https://splunk.github.io/addonfactory-ucc-generator/contributing/#build-and-test)
* [ ] Changes are documented
* [x] PR title and description follows the [contributing
principles](https://splunk.github.io/addonfactory-ucc-generator/contributing/#pull-requests)

splunk_add_on_ucc_framework/install_python_libraries.py

@@ -105,6 +105,10 @@ def _pip_is_lib_installed(
     try:
         my_env = os.environ.copy()
         my_env["PYTHONPATH"] = target
+
+        # Disable writing of .pyc files (__pycache__)
+        my_env["PYTHONDONTWRITEBYTECODE"] = "1"
+
         if allow_higher_version:
             result = _subprocess_run(command=cmd, env=my_env)
             if result.returncode != 0:

tests/smoke/test_ucc_build.py

@@ -190,6 +190,7 @@ def test_ucc_generate_with_everything(caplog):
             ("appserver", "static", "alerticon.png"),
             ("bin", "splunk_ta_uccexample", "modalert_test_alert_helper.py"),
             ("appserver", "static", "js", "build", "entry_page.js.map"),
+            ("lib", "__pycache__"),
         ]
         for af in files_should_be_absent:
             actual_file_path = path.join(actual_folder, *af)

tests/unit/test_install_python_libraries.py

@@ -1,12 +1,16 @@
 import os
 import stat
+from collections import namedtuple
 from typing import List
 from unittest import mock
 
 import pytest
 import tests.unit.helpers as helpers
 from splunk_add_on_ucc_framework.global_config import OSDependentLibraryConfig
 
+from splunk_add_on_ucc_framework import (
+    install_python_libraries as install_python_libraries_module,
+)
 from splunk_add_on_ucc_framework.install_python_libraries import (
     CouldNotInstallRequirements,
     SplunktaucclibNotFound,
@@ -369,11 +373,12 @@ def test_install_libraries_version_mismatch(
         'python3 -m pip show --version cryptography | grep "Version: 41.0.5"'
     )
     mock_subprocess_run.side_effect = (
-        lambda command, shell=True, env=None, capture_output=True: MockSubprocessResult(
-            1
+        lambda command, shell=True, env=None, capture_output=True: (
+            MockSubprocessResult(1)
+            if command == version_mismatch_shell_cmd
+            and ucc_lib_target == env["PYTHONPATH"]
+            else MockSubprocessResult(0)
         )
-        if command == version_mismatch_shell_cmd and ucc_lib_target == env["PYTHONPATH"]
-        else MockSubprocessResult(0)
     )
 
     with pytest.raises(CouldNotInstallRequirements):
@@ -509,6 +514,19 @@ def test_is_pip_lib_installed_wrong_arguments():
         _pip_is_lib_installed("i", "t", "l", allow_higher_version=True)
 
 
+def test_is_pip_lib_installed_do_not_write_bytecode(monkeypatch):
+    Result = namedtuple("Result", ["returncode", "stdout", "stderr"])
+
+    def run(command, env):
+        assert command == "python3 -m pip show --version libname"
+        assert env["PYTHONPATH"] == "target"
+        assert env["PYTHONDONTWRITEBYTECODE"] == "1"
+        return Result(0, b"", b"")
+
+    monkeypatch.setattr(install_python_libraries_module, "_subprocess_run", run)
+    assert _pip_is_lib_installed("python3", "target", "libname")
+
+
 @mock.patch("subprocess.run", autospec=True)
 def test_install_libraries_pip_custom_flag(mock_subprocess_run):
     mock_subprocess_run.return_value = MockSubprocessResult(0)