Upgrade Python from 3.7 to 3.9 (#1531)

Part of tiny-pilot/tinypilot-pro#1002.

[Debian Bullseye ships with Python
3.9](https://packages.debian.org/bullseye/python3), so it’s safe for us
to upgrade our Python requirement from 3.7 to 3.9.

I’ve also fixed the URL anchor in the comment in `db/store.py`, which
was outdated.
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href="https://codeapprove.com/pr/tiny-pilot/tinypilot/1531"><img
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on CodeApprove" /></a>

.circleci/continue_config.yml

@@ -31,7 +31,7 @@ jobs:
           command: ./dev-scripts/check-bash
   lint_sql:
     docker:
-      - image: cimg/python:3.7.4
+      - image: cimg/python:3.9.17
     steps:
       - checkout
       - run:
@@ -68,7 +68,7 @@ jobs:
           command: ./dev-scripts/decode-edid
   build_python:
     docker:
-      - image: cimg/python:3.7.4
+      - image: cimg/python:3.9.17
     steps:
       - checkout
       - run:
@@ -96,12 +96,12 @@ jobs:
     docker:
       # To run tests against the dev server, Playwright needs a CircleCI image
       # with Python, Node, and a browser. While the build_python and
-      # build_javascript steps use python-3.7.4 and node-18.16.1 respectively,
+      # build_javascript steps use python-3.9.17 and node-18.16.1 respectively,
       # the CircleCI image with *both* python and node in the closest versions
-      # is python:3.7.17-browsers. It has python-3.7.17 and node-18.16.0.
+      # is python:3.9.17-browsers. It has python-3.9.17 and node-18.16.0.
       #
       # See: https://circleci.com/developer/images/image/cimg/python#tagging-scheme
-      - image: cimg/python:3.7.17-browsers
+      - image: cimg/python:3.9.17-browsers
     environment:
       NODE_ENV: development
     steps:
@@ -239,7 +239,7 @@ jobs:
             molecule test
   build_bundle:
     docker:
-      - image: cimg/python:3.7.4
+      - image: cimg/python:3.9.17
     steps:
       - checkout
       - attach_workspace:

CONTRIBUTING.md

@@ -8,7 +8,7 @@ The steps below show you how to quickly set up a development environment for Tin
 
 ### Requirements
 
-- Python 3.7 or higher
+- Python 3.9 or higher
 - Node.js 18.16.1 or higher
 - [shellcheck](https://github.com/koalaman/shellcheck#installing)
 - Docker 20.10.x or higher

app/db/store.py

@@ -121,7 +121,7 @@ def create_or_open(db_path):
         with connection as transaction:
             # Without an explicit `BEGIN`, the sqlite3 library would autocommit
             # structural modifications immediately. See:
-            # https://docs.python.org/3.7/library/sqlite3.html#transaction-control
+            # https://docs.python.org/3.9/library/sqlite3.html#controlling-transactions
             # Note that the `BEGIN` cannot be executed in a separate, preceding
             # `transaction.execute('BEGIN')` command, because
             # `transaction.executescript` automatically issues a `COMMIT` before

app/hid/write_test.py

@@ -15,8 +15,8 @@
 # This was observed on a 2021 Macbook Pro M1 Max running OSX Ventura 13.2.1.
 #
 # [1] https://github.com/python/cpython/commit/17a5588740b3d126d546ad1a13bdac4e028e6d50
-# [2] https://docs.python.org/3.11/library/multiprocessing.html#the-spawn-and-forkserver-start-methods
-# [3] https://docs.python.org/3/library/pickle.html#what-can-be-pickled-and-unpickled:~:text=(using%20def%2C%20not%20lambda)
+# [2] https://docs.python.org/3.9/library/multiprocessing.html#the-spawn-and-forkserver-start-methods
+# [3] https://docs.python.org/3.9/library/pickle.html#what-can-be-pickled-and-unpickled:~:text=(using%20def%2C%20not%20lambda)
 
 
 def do_nothing():