Manage Python versions

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: "3.6.0"
  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:

  1. 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        
  2. Create an .environment file:

    touch .environment
  3. 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.