add function for loading plugin modules

Loads modules for configurable code like tokenizers, sanitizers, etc.
Supports internal modules, external libraries and code from the
project directory.

test/python/config/test_config_load_module.py

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# This file is part of Nominatim. (https://nominatim.org)
+#
+# Copyright (C) 2022 by the Nominatim developer community.
+# For a full list of authors see the git log.
+"""
+Test for loading extra Python modules.
+"""
+from pathlib import Path
+import sys
+
+import pytest
+
+from nominatim.config import Configuration
+
+@pytest.fixture
+def test_config(src_dir, tmp_path):
+    """ Create a configuration object with project and config directories
+        in a temporary directory.
+    """
+    (tmp_path / 'project').mkdir()
+    (tmp_path / 'config').mkdir()
+    conf = Configuration(tmp_path / 'project', src_dir / 'settings')
+    conf.config_dir = tmp_path / 'config'
+    return conf
+
+
+def test_load_default_module(test_config):
+    module = test_config.load_plugin_module('version', 'nominatim')
+
+    assert isinstance(module.NOMINATIM_VERSION, tuple)
+
+
+def test_load_plugin_module(test_config, tmp_path):
+    (tmp_path / 'project' / 'testpath').mkdir()
+    (tmp_path / 'project' / 'testpath' / 'mymod.py')\
+        .write_text("def my_test_function():\n  return 'gjwitlsSG42TG%'")
+
+    module = test_config.load_plugin_module('testpath/mymod.py', 'private.something')
+
+    assert module.my_test_function() == 'gjwitlsSG42TG%'
+
+    # also test reloading module
+    (tmp_path / 'project' / 'testpath' / 'mymod.py')\
+        .write_text("def my_test_function():\n  return 'hjothjorhj'")
+
+    module = test_config.load_plugin_module('testpath/mymod.py', 'private.something')
+
+    assert module.my_test_function() == 'gjwitlsSG42TG%'
+
+
+def test_load_external_library_module(test_config, tmp_path, monkeypatch):
+    MODULE_NAME = 'foogurenqodr4'
+    pythonpath = tmp_path / 'priv-python'
+    pythonpath.mkdir()
+    (pythonpath / MODULE_NAME).mkdir()
+    (pythonpath / MODULE_NAME / '__init__.py').write_text('')
+    (pythonpath / MODULE_NAME / 'tester.py')\
+        .write_text("def my_test_function():\n  return 'gjwitlsSG42TG%'")
+
+    monkeypatch.syspath_prepend(pythonpath)
+
+    module = test_config.load_plugin_module(f'{MODULE_NAME}.tester', 'private.something')
+
+    assert module.my_test_function() == 'gjwitlsSG42TG%'
+
+    # also test reloading module
+    (pythonpath / MODULE_NAME / 'tester.py')\
+        .write_text("def my_test_function():\n  return 'dfigjreigj'")
+
+    module = test_config.load_plugin_module(f'{MODULE_NAME}.tester', 'private.something')
+
+    assert module.my_test_function() == 'gjwitlsSG42TG%'
+
+    del sys.modules[f'{MODULE_NAME}.tester']