Use python3 as the canonical command name course-wide (#104) (#105)

modules/17-secrets-config-and-environments/README.md

@@ -90,10 +90,10 @@ Set one for a single command:
 
 ```bash
 # macOS / Linux
-TASKS_API_KEY="sk-live-..." python sync.py
+TASKS_API_KEY="sk-live-..." python3 sync.py
 
 # Windows PowerShell
-$env:TASKS_API_KEY="sk-live-..."; python sync.py
+$env:TASKS_API_KEY="sk-live-..."; python3 sync.py
 ```
 
 Read it back in code, and **fail loudly if it's missing**, because a silent empty string is worse
@@ -307,7 +307,7 @@ type the commands by hand. Then you'll make it select config per environment.
 
    ```bash
    cd ~/ai-workflow-course/tasks-app
-   python sync.py
+   python3 sync.py
    ```
 
    It prints a simulated request, including `Authorization: Bearer sk-live-...`. Open `sync.py` and
@@ -407,7 +407,7 @@ type the commands by hand. Then you'll make it select config per environment.
 5. Run it reading from your `.env`:
 
    ```bash
-   python sync.py                # loads .env -> dev URL, key from the file
+   python3 sync.py                # loads .env -> dev URL, key from the file
    ```
 
 6. Now prove the 12-factor point: **same code, different environment, no edit.** Override at the
@@ -415,13 +415,13 @@ type the commands by hand. Then you'll make it select config per environment.
 
    ```bash
    # macOS / Linux
-   APP_ENV=staging python sync.py
-   APP_ENV=prod    TASKS_API_KEY="sk-live-prod-key" python sync.py
+   APP_ENV=staging python3 sync.py
+   APP_ENV=prod    TASKS_API_KEY="sk-live-prod-key" python3 sync.py
    ```
 
    ```powershell
    # Windows PowerShell
-   $env:APP_ENV="staging"; python sync.py
+   $env:APP_ENV="staging"; python3 sync.py
    ```
 
    Watch the backend URL change with `APP_ENV` while the source never does. That's config in the
@@ -483,7 +483,7 @@ left behind a `.env.example` so the next person (or agent) knows what to supply.
 - `sync.py` runs entirely from the environment, and `grep "sk-live" sync.py` prints nothing.
 - A real `.env` exists, contains your secret, and does **not** appear in `git status`, while
   `.env.example` is tracked.
-- `APP_ENV=staging python sync.py` and the default run hit different backend URLs with **zero**
+- `APP_ENV=staging python3 sync.py` and the default run hit different backend URLs with **zero**
   source edits between them.
 - You can state, in one sentence, why deleting a committed secret and re-committing does not fix the
   leak, and what the actual fix is (rotation).

modules/17-secrets-config-and-environments/lab/starter/sync.py

@@ -11,7 +11,7 @@ Your job in the lab is to refactor BOTH out of the source and into the environme
 ahead and fix it yet; first run it as-is so you can see the smell.
 
 Run it:
-    python sync.py
+    python3 sync.py
 
 It does not actually hit the network (so the lab works offline, on any OS); it simulates the
 request and prints what it *would* send.