Plugin development

This section addresses the development of and with the csspin-python plugin-package.

How does a plugin define Python dependencies?

A plugin that depends on python can depend on other Python packages. These plugin-specific dependencies can be defined using requires.python.

Dependencies are installed while executing spin provision and can then be used within any function of the plugin.

Declaring Python dependencies of a dummy plugin

from csspin import config


defaults = config(
    requires=config(
        spin=["csspin_python.python"],
        python=["requests"],
    ),
)


def configure():
    """Configuring the dummy plugin"""
    import requests

    ...


def dummy():
    """This is a dummy plugin"""
    ...

How to write environment variables into the Python virtual environment?

spin’s API already provides the csspin.setenv function that enables setting environment variables for the current process.

In combination with the python plugin, these environment variables are written into the Python virtual environment in case the plugin depends on python and csspin.setenv is called during configure(cfg) or provision(cfg) of the current plugin.

Writing environment variables into the Python virtual environment

from csspin import config, setenv

defaults = config(spin=["csspin_python.python"])


def configure(cfg):
    setenv(FOO="bar")


def provision(cfg):
    setenv(PIPAPO="...")
    ...


...

After provision of a project using the plugin module above, the environment variable FOO is available within the Python virtual environment, i.e. also when activating the virtual environment manually. This is useful for such environment variables that are required by plugins during runtime and don’t change when working with the same environment.

What is the use of ProvisionerProtocol?

Python packages are installed through a provisioner, which is responsible for the dependency management strategy.

The python plugin implements a ProvisionerProtocol interface that forms the base of the default provisioner SimpleProvisioner, which is using the Python package manager pip to install and manage Python dependencies.