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.

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

Specifying the CPython version through buildpack.yml configuration will be deprecated in CPython Buildpack v1.0.0.

To migrate from using buildpack.yml please set the following environment variables at build time either directly or through a project.toml file.

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 my-app --env BP_CPYTHON_VERSION=3.6.*

[build]
  [[build.env]]
    name = 'BP_CPYTHON_VERSION'
    value = '3.6.*' # any valid semver constraints (e.g. 3.6.7, 3.*) are acceptable

cpython:
  # this allows you to specify a version constraint for the python depdendency
  # any valid semver constraints (e.g. 3.*) are also acceptable
  version: ~3

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

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