Python: Add load_dotenv() to samples for .env file support (#4043)

* Initial plan

* Add load_dotenv() to 303 Python samples for environment variable loading

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Update SAMPLE_GUIDELINES.md to document load_dotenv() requirement

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Update samples README.md to document .env file usage

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Run ruff format on all changed sample files

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Clarify load_dotenv() usage in README - local dev vs production

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Remove deprecated getting_started folder as requested

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Document env_file_path parameter for per-client configuration

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Merge main branch to resolve conflicts

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Fix run_evaluation.py file that was empty in merge commit

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Remove dotnet changes from merge - out of scope for this PR

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Remove package and test changes from merge - only sample changes needed

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Remove test_func_utils.py - only sample changes needed

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Revert sample files not in original changeset - keep only load_dotenv additions

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Move load_dotenv() outside snippet tag in 06_host_your_agent.py

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Fix comment placement - move load_dotenv before code comments

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Fix load_dotenv() placement across all samples - after docstring, before code comments

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Merge latest main branch with load_dotenv changes

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Remove non-sample changes from merge - keep only load_dotenv additions

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Revert non-load_dotenv sample changes from merge

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Fix run_evaluation.py - use main's improved version (file already had load_dotenv)

Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>

* Manual update

* Manual update 2

* Fix Role usage and load_dotenv placement per PR review feedback

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Fix Role usage - use string literals not enum attributes

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Fix SAMPLE_GUIDELINES.md example - load_dotenv before docstring per guidance

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Move load_dotenv() before docstrings in all samples per SAMPLE_GUIDELINES ordering

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Address PR review: rename files, fix placement, add session usage, remove note

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

* Update Redis README to reference renamed file redis_history_provider.py

Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: TaoChenOSU <12570346+TaoChenOSU@users.noreply.github.com>
Co-authored-by: Tao Chen <taochen@microsoft.com>
Co-authored-by: eavanvalkenburg <13749212+eavanvalkenburg@users.noreply.github.com>
Co-authored-by: Eduard van Valkenburg <eavanvalkenburg@users.noreply.github.com>

python/samples/SAMPLE_GUIDELINES.md

@@ -8,11 +8,12 @@ Every sample file should follow this order:
 
 1. PEP 723 inline script metadata (if external dependencies are needed)
 2. Copyright header: `# Copyright (c) Microsoft. All rights reserved.`
-3. Required imports
-4. Module docstring: `"""This sample demonstrates..."""`
-5. Helper functions
-6. Main function(s) demonstrating functionality
-7. Entry point: `if __name__ == "__main__": asyncio.run(main())`
+3. Required imports (including `from dotenv import load_dotenv`)
+4. Environment variable loading: `load_dotenv()`
+5. Module docstring: `"""This sample demonstrates..."""`
+6. Helper functions
+7. Main function(s) demonstrating functionality
+8. Entry point: `if __name__ == "__main__": asyncio.run(main())`
 
 When modifying samples, update associated README files in the same or parent folders.
 
@@ -35,6 +36,30 @@ When samples depend on external packages not included in the dev environment (e.
 
 This makes samples self-contained and runnable without installing extra packages into the dev environment. Do not add sample-only dependencies to the root `pyproject.toml` dev group.
 
+## Environment Variables
+
+All samples that use environment variables (API keys, endpoints, etc.) must call `load_dotenv()` at the beginning of the file to load variables from a `.env` file. The `python-dotenv` package is already included as a dependency of `agent-framework-core`.
+
+```python
+# Copyright (c) Microsoft. All rights reserved.
+
+import asyncio
+import os
+
+from agent_framework.azure import AzureOpenAIResponsesClient
+from azure.identity import AzureCliCredential
+from dotenv import load_dotenv
+
+# Load environment variables from .env file
+load_dotenv()
+
+"""
+Sample docstring explaining what the sample does.
+"""
+```
+
+Users can create a `.env` file in the `python/` directory based on `.env.example` to set their environment variables without having to export them in their shell.
+
 ## Syntax Checking
 
 Run `uv run poe samples-syntax` to check samples for syntax errors and missing imports from `agent_framework`. This uses a relaxed pyright configuration that validates imports without strict type checking.
@@ -75,12 +100,12 @@ For the getting started samples and the concept samples, we should have the foll
 2. A summary should be included underneath the imports that explains the purpose of the sample and required components/concepts to understand the sample. For example:
 
     ```python
-    '''
+    """
     This sample shows how to create a chatbot. This sample uses the following two main components:
     - a ChatCompletionService: This component is responsible for generating responses to user messages.
     - a ChatHistory: This component is responsible for keeping track of the chat history.
     The chatbot in this sample is called Mosscap, who responds to user messages with long flowery prose.
-    '''
+    """
     ```
 
 3. Mark the code with comments to explain the purpose of each section of the code. For example:
@@ -98,13 +123,13 @@ For the getting started samples and the concept samples, we should have the foll
 4. At the end of the sample, include a section that explains the expected output of the sample. For example:
 
     ```python
-    '''
+    """
     Sample output:
     User:> Why is the sky blue in one sentence?
     Mosscap:> The sky is blue due to the scattering of sunlight by the molecules in the Earth's atmosphere,
     a phenomenon known as Rayleigh scattering, which causes shorter blue wavelengths to become more
     prominent in our visual perception.
-    '''
+    """
     ```
 
 For the demos, a README.md file must be included that explains the purpose of the demo and how to run it. The README.md file should include the following: