Python: Create an experimental class and function decorator. (#6298)

### Motivation and Context

There may be classes or functions inside of SK Python that should be
deemed as experimental. Currently in Python there is no out-of-the-box
way to get the decorator.

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### Description

As there is a name clash with using `experimental` as the decorator
name, we are introducing two decorators: one `experimental_class` and
one `experimental_function`. The note that "This {function | class} is
experimental and may change in the future" is included in the docstring
and a bool `is_experimental` on the class is added.

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone 😄

python/semantic_kernel/utils/experimental_decorator.py

@@ -0,0 +1,28 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+import types
+from typing import Callable, Type
+
+
+def experimental_function(func: Callable) -> Callable:
+    if isinstance(func, types.FunctionType):
+        if func.__doc__:
+            func.__doc__ += "\n\nNote: This function is experimental and may change in the future."
+        else:
+            func.__doc__ = "Note: This function is experimental and may change in the future."
+
+        func.is_experimental = True
+
+    return func
+
+
+def experimental_class(cls: Type) -> Type:
+    if isinstance(cls, type):
+        if cls.__doc__:
+            cls.__doc__ += "\n\nNote: This class is experimental and may change in the future."
+        else:
+            cls.__doc__ = "Note: This class is experimental and may change in the future."
+
+        cls.is_experimental = True
+
+    return cls

python/tests/conftest.py

@@ -94,6 +94,20 @@ def decorated_native_function(self) -> str:
     return CustomPlugin
 
 
+@pytest.fixture(scope="session")
+def experimental_plugin_class():
+    from semantic_kernel.functions.kernel_function_decorator import kernel_function
+    from semantic_kernel.utils.experimental_decorator import experimental_class
+
+    @experimental_class
+    class ExperimentalPlugin:
+        @kernel_function(name="getLightStatus")
+        def decorated_native_function(self) -> str:
+            return "test"
+
+    return ExperimentalPlugin
+
+
 @pytest.fixture(scope="session")
 def create_mock_function() -> Callable:
     from semantic_kernel.contents.streaming_text_content import StreamingTextContent

python/tests/unit/functions/test_kernel_experimental_decorator.py

@@ -0,0 +1,31 @@
+# # Copyright (c) Microsoft. All rights reserved.
+
+from semantic_kernel.utils.experimental_decorator import (
+    experimental_function,
+)
+
+
+@experimental_function
+def my_function() -> None:
+    """This is a sample function docstring."""
+    pass
+
+
+@experimental_function
+def my_function_no_doc_string() -> None:
+    pass
+
+
+def test_function_experimental_decorator() -> None:
+    assert (
+        my_function.__doc__
+        == "This is a sample function docstring.\n\nNote: This function is experimental and may change in the future."
+    )  # noqa: E501
+    assert hasattr(my_function, "is_experimental")
+    assert my_function.is_experimental is True
+
+
+def test_function_experimental_decorator_with_no_doc_string() -> None:
+    assert my_function_no_doc_string.__doc__ == "Note: This function is experimental and may change in the future."
+    assert hasattr(my_function_no_doc_string, "is_experimental")
+    assert my_function_no_doc_string.is_experimental is True

python/tests/unit/functions/test_kernel_function_decorators.py

@@ -1,3 +1,5 @@
+# Copyright (c) Microsoft. All rights reserved.
+
 from typing import TYPE_CHECKING, Annotated, Any, AsyncGenerator, AsyncIterable, Optional, Union
 
 import pytest

python/tests/unit/kernel/test_kernel.py

@@ -589,4 +589,14 @@ def test_instantiate_prompt_execution_settings_through_kernel(kernel_with_servic
     assert settings.service_id == "service"
 
 
+# endregion
+# experimental class decorator
+
+
+def test_experimental_class_has_decorator_and_flag(experimental_plugin_class):
+    assert hasattr(experimental_plugin_class, "is_experimental")
+    assert experimental_plugin_class.is_experimental
+    assert "This class is experimental and may change in the future." in experimental_plugin_class.__doc__
+
+
 # endregion