Update python to use %%IMAGE%% (and unroll onbuild examples)

python/content.md

@@ -11,19 +11,33 @@ Python is an interpreted, interactive, object-oriented, open-source programming
 ## Create a `Dockerfile` in your Python app project
 
 ```dockerfile
-FROM python:3-onbuild
+FROM %%IMAGE%%:3
+
+WORKDIR /usr/src/app
+
+COPY requirements.txt ./
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
 CMD [ "python", "./your-daemon-or-script.py" ]
 ```
 
 or (if you need to use Python 2):
 
 ```dockerfile
-FROM python:2-onbuild
+FROM %%IMAGE%%:2
+
+WORKDIR /usr/src/app
+
+COPY requirements.txt ./
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY . .
+
 CMD [ "python", "./your-daemon-or-script.py" ]
 ```
 
-These images include multiple `ONBUILD` triggers, which should be all you need to bootstrap most applications. The build will `COPY` a `requirements.txt` file, `RUN pip install` on said file, and then copy the current directory into `/usr/src/app`.
-
 You can then build and run the Docker image:
 
 ```console
@@ -36,11 +50,11 @@ $ docker run -it --rm --name my-running-app my-python-app
 For many simple, single file projects, you may find it inconvenient to write a complete `Dockerfile`. In such cases, you can run a Python script by using the Python Docker image directly:
 
 ```console
-$ docker run -it --rm --name my-running-script -v "$PWD":/usr/src/myapp -w /usr/src/myapp python:3 python your-daemon-or-script.py
+$ docker run -it --rm --name my-running-script -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:3 python your-daemon-or-script.py
 ```
 
 or (again, if you need to use Python 2):
 
 ```console
-$ docker run -it --rm --name my-running-script -v "$PWD":/usr/src/myapp -w /usr/src/myapp python:2 python your-daemon-or-script.py
+$ docker run -it --rm --name my-running-script -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:2 python your-daemon-or-script.py
 ```