docs: align contributor Python version docs with package metadata (#9047)

* docs: align contributor Python version guidance

* docs: fix stale virtualenv example in dev guide

Author: immanuwell

CONTRIBUTING.md

@@ -43,7 +43,7 @@ Contributions via pull requests are much appreciated. Before sending us a pull r
 1. You are working against the latest source on the *develop* branch.
 2. You check existing open, and recently merged, pull requests to make sure someone else hasn't addressed the problem already.
 3. You open an issue to discuss any significant work - we would hate for your time to be wasted.
-4. The change works in Python3 (see supported Python Versions in setup.py)
+4. The change works in supported Python versions (see `pyproject.toml` and CI workflows)
 5. Does the PR have updated/added unit, functional, and integration tests?
 6. PR is merged submitted to merge into develop.
 

DEVELOPMENT_GUIDE.md

@@ -20,7 +20,7 @@ Gitpod is free for 50 hours per month - make sure to stop your workspace when yo
 ## Environment Setup
 ### 1. Prerequisites (Python Virtual Environment)
 
-AWS SAM CLI is mainly written in Python 3 and we support Python 3.8 and above.
+AWS SAM CLI is mainly written in Python 3 and currently requires Python 3.10 and above.
 So, having a Python environment with this version is required.
 
 Having a dedicated Python virtual environment ensures it won't "pollute" or get "polluted" 
@@ -64,10 +64,10 @@ exec $SHELL  # restart your shell to enable pyenv-virtualenv
 Next, setup a virtual environment and activate it:
 
 ```sh
-# Assuming you want to develop AWS SAM CLI in Python 3.8.9
-pyenv install 3.8.9  # install Python 3.8.9 using pyenv
-pyenv virtualenv 3.8.9 samcli38  # create a virtual environment using 3.8.9 named "samcli38"
-pyenv activate samcli38  # activate the virtual environment
+# Assuming you want to develop AWS SAM CLI in Python 3.10.19
+pyenv install 3.10.19  # install Python 3.10.19 using pyenv
+pyenv virtualenv 3.10.19 samcli310  # create a virtual environment using 3.10.19 named "samcli310"
+pyenv activate samcli310  # activate the virtual environment
 ```
 
 ### 2. Initialize dependencies and create `samdev` available in `$PATH`
@@ -142,7 +142,7 @@ Make sure you are in the same virtual environment as the one you are using with
 ```sh
 source <sam-cli-directory-path>/.venv/bin/activate  # if you chose to use venv to setup the virtual environment
 # or
-pyenv activate samcli38  # if you chose to use pyenv to setup the virtual environment
+pyenv activate samcli310  # if you chose to use pyenv to setup the virtual environment
 ```
 
 Install the SAM Transformer in editable mode so that 
@@ -173,27 +173,27 @@ contribute to the repository, there are a few more things to consider.
 
 ### Make Sure AWS SAM CLI Work in Multiple Python Versions
 
-We support version 3.8 and above. Our CI/CD pipeline is setup to run
-unit tests against all Python versions. So make sure you test it
-with all versions before sending a Pull Request.
+We support version 3.10 and above. Our PR workflow runs on Python 3.10 and 3.11,
+and our integration workflows install additional Python versions to cover Lambda runtime scenarios.
+So make sure you test your change against supported Python versions before sending a Pull Request.
 See [Unit testing with multiple Python versions](#unit-testing-with-multiple-python-versions-optional). 
-This is most important if you are developing in a Python version greater than the minimum supported version (currently 3.8), as any new features released in 3.9+ will not work.
+This is most important if you are developing in a Python version greater than the minimum supported version (currently 3.10), as any new features released in higher versions will not work on the minimum supported version.
 
 If you chose to use `pyenv` in the previous session, setting up a 
 different Python version should be easy:
 
-(assuming you are in virtual environment named `samcli39` with Python version 3.9.x)
+(assuming you are in virtual environment named `samcli311` with Python version 3.11.x)
 
 ```sh
-# Your shell now should look like "(samcli39) $"
-pyenv deactivate samcli39  # "(samcli39)" will disappear
-pyenv install 3.8.9  # one time setup
-pyenv virtualenv 3.8.9 samcli38  # one time setup
-pyenv activate samcli38
-# Your shell now should look like "(samcli38) $"
+# Your shell now should look like "(samcli311) $"
+pyenv deactivate samcli311  # "(samcli311)" will disappear
+pyenv install 3.10.19  # one time setup
+pyenv virtualenv 3.10.19 samcli310  # one time setup
+pyenv activate samcli310
+# Your shell now should look like "(samcli310) $"
 
 # You can verify the version of Python
-python --version  # Python 3.8.9
+python --version  # Python 3.10.19
 
 make init  # one time setup, this will put a file `samdev` available in $PATH
 ```
@@ -202,8 +202,8 @@ For Windows, use your favorite tool for managing different python versions and e
 
 ### Format Python Code
 
-We format our code using [Black](https://github.com/python/black) and verify the source code is
-black compliant in AppVeyor during PRs. Black will be installed automatically with `make init` or `./Make -Init` on Windows.
+We format our code using [Black](https://github.com/python/black) and verify the source code in GitHub Actions during PRs.
+Black will be installed automatically with `make init` or `./Make -Init` on Windows.
 
 There are generally 3 options to make sure your change is compliant with our formatting standard:
 
@@ -235,11 +235,11 @@ and this will happen:
 pyenv: black: command not found
 
 The `black' command exists in these Python versions:
-  3.8.9/envs/samcli38
-  samcli38
+  3.10.19/envs/samcli310
+  samcli310
 ``` 
 
-A simple workaround is to use `/Users/<username>/.pyenv/versions/samcli37/bin/black` 
+A simple workaround is to use `/Users/<username>/.pyenv/versions/samcli310/bin/black`
 instead of `/Users/<username>/.pyenv/shims/black`.
 
 #### (Option 3) Pre-commit
@@ -265,12 +265,12 @@ We also suggest to run `make pr` or `./Make -pr` in all Python versions.
 
 #### Unit Testing with Multiple Python Versions (Optional)
 
-Currently, SAM CLI only supports Python3 versions (see setup.py for exact versions). For the most
-part, code that works in Python3.8 will work in Python3.9. You only run into problems if you are
-trying to use features released in a higher version (for example features introduced into Python3.9
-will not work in Python3.8). If you want to test in many versions, you can create a virtualenv for
-each version and flip between them (sourcing the activate script). Typically, we run all tests in
-one python version locally and then have our ci (appveyor) run all supported versions.
+Currently, SAM CLI supports Python 3.10 and above (see `pyproject.toml` for package metadata and
+`.github/workflows/build.yml` for the PR test matrix). For the most part, code that works in Python 3.10
+will work in Python 3.11. You only run into problems if you are trying to use features released in a
+higher version that do not exist in the minimum supported version. If you want to test in many versions,
+you can create a virtualenv for each version and flip between them (sourcing the activate script).
+Typically, we run tests in one Python version locally and let CI cover the supported matrix.
 
 #### Integration Test (Optional)