Don't run pip install -r requirements.txt in the Dockerfile

Instead, make it a suggested postCreateCommand.

containers/python-3/.devcontainer/Dockerfile

@@ -13,11 +13,10 @@ ARG USERNAME=vscode
 ARG USER_UID=1000
 ARG USER_GID=$USER_UID
 
-# Copy requirements.txt (if found) to a temp location so we can install it. The `*`
-# is required so COPY doesn't think that part of the command should fail is nothing is
-# found. Also copy "noop.txt" so the COPY instruction copies _something_ to guarantee
-# success somehow.
-COPY *requirements.txt .devcontainer/noop.txt /tmp/pip-tmp/
+# Uncomment the following COPY line and the corresponding lines in the `RUN` command if you wish to
+# include your requirements in the image itself. It is suggested that you only do this if your
+# requirements rarely (if ever) change.
+# COPY requirements.txt /tmp/pip-tmp/
 
 # Configure apt and install packages
 RUN apt-get update \
@@ -29,9 +28,9 @@ RUN apt-get update \
     # Install pylint
     && pip --disable-pip-version-check --no-cache-dir install pylint \
     #
-    # Update Python environment based on requirements.txt (if presenet)
-    && if [ -f "/tmp/pip-tmp/requirements.txt" ]; then pip --disable-pip-version-check --no-cache-dir install -r /tmp/pip-tmp/requirements.txt; fi \
-    && rm -rf /tmp/pip-tmp \
+    # Update Python environment based on requirements.txt
+    # && pip --disable-pip-version-check --no-cache-dir install -r /tmp/pip-tmp/requirements.txt \
+    # && rm -rf /tmp/pip-tmp \
     #
     # Create a non-root user to use if preferred - see https://aka.ms/vscode-remote/containers/non-root-user.
     && groupadd --gid $USER_GID $USERNAME \

containers/python-3/.devcontainer/devcontainer.json

@@ -7,7 +7,7 @@
 	// "appPort": [],
 
 	// Uncomment the next line to run commands after the container is created.
-	// "postCreateCommand": "python --version",
+	// "postCreateCommand": "pip install -r requirements.txt",
 
 	// Uncomment the next line to use a non-root user. See https://aka.ms/vscode-remote/containers/non-root-user.
 	// "runArgs": [ "-u", "1000" ],

containers/python-3/README.md

@@ -2,17 +2,17 @@
 
 ## Summary
 
-*Develop Python 3 applications. Installs dependencies from your requirements.txt file and the Python extension.*
+*Develop Python 3 applications.*
 
-| Metadata | Value |  
+| Metadata | Value |
 |----------|-------|
 | *Contributors* | The [VS Code Python extension](https://marketplace.visualstudio.com/itemdetails?itemName=ms-python.python) team |
 | *Definition type* | Dockerfile |
 | *Languages, platforms* | Python |
 
 ## Using this definition with an existing folder
 
-For convenience, this definition will automatically install dependencies from your `requirements.txt` file when the container is built. Also note that only the integrated terminal is supported by the Remote - Containers extension. You may need to modify `launch.json` configurations to include the following value if an external console is used.
+Note that only the integrated terminal is supported by the Remote - Containers extension. You may need to modify `launch.json` configurations to include the following value if an external console is used.
 
 ```json
 "console": "integratedTerminal"