Python: custom service selector sample (microsoft#6802)

### Motivation and Context

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### Description

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### Contribution Checklist

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

Author: eavanvalkenburg

python/samples/concepts/README.md

@@ -17,5 +17,6 @@ This section contains code snippets that demonstrate the usage of Semantic Kerne
 | PromptTemplates | Using [`Templates`](https://github.com/microsoft/semantic-kernel/blob/main/python/semantic_kernel/prompt_template/prompt_template_base.py) with parametrization for `Prompt` rendering  |
 | RAG | Different ways of `RAG` (Retrieval-Augmented Generation) |
 | Search | Using search services information |
+| Service Selector | Shows how to create and use a custom service selector class. |
 | Setup | How to setup environment variables for Semantic Kernel |
 | TextGeneration | Using [`TextGeneration`](https://github.com/microsoft/semantic-kernel/blob/main/python/semantic_kernel/connectors/ai/text_completion_client_base.py) capable service with models  |

python/samples/concepts/service_selector/custom_service_selector.py

@@ -0,0 +1,73 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+from semantic_kernel.connectors.ai.open_ai.services.azure_chat_completion import AzureChatCompletion
+from semantic_kernel.connectors.ai.open_ai.services.open_ai_chat_completion import OpenAIChatCompletion
+from semantic_kernel.connectors.ai.prompt_execution_settings import PromptExecutionSettings
+from semantic_kernel.const import DEFAULT_SERVICE_NAME
+from semantic_kernel.contents.chat_history import ChatHistory
+from semantic_kernel.functions.kernel_arguments import KernelArguments
+from semantic_kernel.functions.kernel_function import KernelFunction
+from semantic_kernel.kernel import Kernel
+from semantic_kernel.kernel_types import AI_SERVICE_CLIENT_TYPE
+from semantic_kernel.services.ai_service_client_base import AIServiceClientBase
+from semantic_kernel.services.ai_service_selector import AIServiceSelector
+from semantic_kernel.services.kernel_services_extension import KernelServicesExtension
+
+
+class CustomServiceSelector(AIServiceSelector):
+    def select_ai_service(
+        self,
+        kernel: "KernelServicesExtension",
+        function: "KernelFunction",
+        arguments: "KernelArguments",
+        type_: type[AI_SERVICE_CLIENT_TYPE] | tuple[type[AI_SERVICE_CLIENT_TYPE], ...] | None = None,
+    ) -> tuple["AIServiceClientBase", "PromptExecutionSettings"]:
+        execution_settings_dict = arguments.execution_settings or {}
+        if func_exec_settings := getattr(function, "prompt_execution_settings", None):
+            for id, settings in func_exec_settings.items():
+                if id not in execution_settings_dict:
+                    execution_settings_dict[id] = settings
+        if not execution_settings_dict:
+            from semantic_kernel.connectors.ai.prompt_execution_settings import PromptExecutionSettings
+
+            execution_settings_dict = {DEFAULT_SERVICE_NAME: PromptExecutionSettings()}
+
+        gpt_4_settings = {
+            service_name: settings
+            for service_name, settings in execution_settings_dict.items()
+            if "gpt-4" in service_name
+        }
+        if gpt_4_settings:
+            service_id = list(gpt_4_settings.keys())[0]
+            service = kernel.get_service(service_id, type=type_)
+            service_settings = service.get_prompt_execution_settings_from_settings(gpt_4_settings[service_id])
+            return service, service_settings
+        return super().select_ai_service(kernel, function, arguments, type_)
+
+
+kernel = Kernel(ai_service_selector=CustomServiceSelector())
+kernel.add_service(AzureChatCompletion(service_id="gpt-4o"))
+kernel.add_service(OpenAIChatCompletion(service_id="gpt-3.5-turbo", ai_model_id="gpt-3.5-turbo"))
+
+kernel.add_function(
+    plugin_name="selector",
+    function_name="select_ai_service",
+    prompt="Always respond with your name. {{$chat_history}}",
+    prompt_execution_settings={
+        "gpt-4o": PromptExecutionSettings(service_id="gpt-4o", max_tokens=200, temperature=0.0),
+        "gpt-3.5-turbo": PromptExecutionSettings(service_id="gpt-3.5-turbo", max_tokens=400, temperature=1.0),
+    },
+)
+
+
+async def main():
+    chat_history = ChatHistory()
+    chat_history.add_user_message("I'm Eduard.")
+    result = await kernel.invoke(plugin_name="selector", function_name="select_ai_service", chat_history=chat_history)
+    print(result)
+
+
+if __name__ == "__main__":
+    import asyncio
+
+    asyncio.run(main())

python/tests/samples/test_concepts.py

@@ -39,6 +39,7 @@
 from samples.concepts.prompt_templates.template_language import main as template_language
 from samples.concepts.rag.rag_with_text_memory_plugin import main as rag_with_text_memory_plugin
 from samples.concepts.search.bing_search_plugin import main as bing_search_plugin
+from samples.concepts.service_selector.custom_service_selector import main as custom_service_selector
 from tests.samples.test_samples_utils import retry
 
 concepts = [
@@ -79,6 +80,7 @@
     param(rag_with_text_memory_plugin, [], id="rag_with_text_memory_plugin"),
     param(bing_search_plugin, [], id="bing_search_plugin"),
     param(azure_chat_image_input, [], id="azure_chat_image_input"),
+    param(custom_service_selector, [], id="custom_service_selector"),
 ]