Paketo CPython Cloud Native Buildpack

The CPython Buildpack provides CPython (reference implementation of Python) 3. The buildpack installs CPython onto the $PATH which makes it available for subsequent buildpacks and in the final running container. It also sets the $PYTHONPATH environment variable.

The buildpack is published for consumption at gcr.io/paketo-buildpacks/cpython and paketobuildpacks/cpython.

Behavior

This buildpack always participates.

The buildpack will do the following:

• At build time:
  • Contributes cpython to a layer
  • Sets the PYTHONPATH to the cpython layer path.
  • Adds the newly installed cpython bin dir location to PATH
• At run time:
  • Does nothing

Configuration

BP_CPYTHON_VERSION

The BP_CPYTHON_VERSION variable allows you to specify the version of CPython that is installed. (Available versions can be found in the buildpack.toml.)

pack build flag

pack build my-app --env BP_CPYTHON_VERSION=3.8.*

In a project.toml

[build]
  [[build.env]]
    name = 'BP_CPYTHON_VERSION'
    value = '3.8.*' # any valid semver constraints (e.g. 3.8.7, 3.*) are acceptable

Integration

The CPython Buildpack provides cpython as a dependency. Downstream buildpacks, can require the cpython dependency by generating Build Plan TOML file that looks like the following:

[[requires]]
  # The name of the CPython dependency is "cpython". This value is considered
  # part of the public API for the buildpack and will not change without a plan
  # for deprecation.
  name = "cpython"
  # The version of the CPython dependency is not required. In the case it
  # is not specified, the buildpack will provide the default version, which can
  # be seen in the buildpack.toml file.
  # If you wish to request a specific version, the buildpack supports
  # specifying a semver constraint in the form of "3.*", "3.8.*", or even
  # "3.8.2".
  version = "3.8.2"
  # The CPython buildpack supports some non-required metadata options.
  [requires.metadata]

    # Setting the build flag to true will ensure that the CPython
    # depdendency is available on the $PATH for subsequent buildpacks during
    # their build phase. If you are writing a buildpack that needs to use CPython
    # during its build process, this flag should be set to true.
    build = true

    # Setting the launch flag to true will ensure that cpython is
    # available to the running application. If you are writing an application
    # that needs to run cpython at runtime, this flag should be set to true.
    launch = true

Usage

To package this buildpack for consumption:

$ ./scripts/package.sh --version <version-number>

This will create a buildpackage.cnb file under the build directory which you can use to build your app as follows: pack build <app-name> -p <path-to-app> -b build/buildpackage.cnb -b <other-buildpacks..>

To run the unit and integration tests for this buildpack:

$ ./scripts/unit.sh && ./scripts/integration.sh