Manage Python versions in non-Python containers

You may need to use a specific version of Python that isn’t available in an app container for a different language. For example, a container might have a long-term support version, while you want the latest version.

In such cases, use the Pyenv version manager to install the specific version you want to use.

1. Add your target Python version as a variable:

   .platform.app.yaml

   variables:
     env:
       # Update for your desired Python version.
       PYTHON_VERSION: "3.11.0"

2. Add Pyenv in a build hook:

   .platform.app.yaml

   hooks:
     build: |
       # Exit the hook on any failure
       set -e
   
       # Clone Pyenv to the build cache if not present
       if [ ! -d "$PLATFORM_CACHE_DIR/.pyenv" ]; then
           mkdir -p $PLATFORM_CACHE_DIR/.pyenv
           git clone https://github.com/pyenv/pyenv.git $PLATFORM_CACHE_DIR/.pyenv
       fi
   
       # Pyenv environment variables
       export PYENV_ROOT="$PLATFORM_CACHE_DIR/.pyenv"
       export PATH="$PYENV_ROOT/bin:$PATH"
   
       # Initialize Pyenv
       if command -v pyenv 1>/dev/null 2>&1; then
           eval "$(pyenv init --path)"
       fi
   
       # Install desired Python version
       mkdir -p $PLATFORM_CACHE_DIR/.pyenv/versions
       if [ ! -d "$PLATFORM_CACHE_DIR/.pyenv/versions/$PYTHON_VERSION" ]; then
           pyenv install $PYTHON_VERSION
       fi
   
       # Set global Python version
       pyenv global $PYTHON_VERSION    

   Now your build hook can use the specified version of Python. You can verify this by running python --version.

   If you want this Python version to be available in the runtime environment, follow these steps:

3. Copy Pyenv to your runtime environment at the end of your build hook:

   .platform.app.yaml

   hooks:
     build: |
       ...
   
       # Copy Pyenv directory to runtime directory
       cp -R $PLATFORM_CACHE_DIR/.pyenv $PLATFORM_APP_DIR
   
       # Rehash Pyenv for new (runtime) location
       PYENV_ROOT="$PLATFORM_APP_DIR/.pyenv" $PLATFORM_APP_DIR/.pyenv/bin/pyenv rehash    

4. Create an .environment file:

   touch .environment

5. Update the PATH for the runtime environment:

   .environment

   export PATH=/app/.pyenv/bin:/app/.pyenv/shims:$PATH

   Now the specified Python version is used in the runtime environment.