Luigi OpenerTarget

Target types are often used directly in the output function, as shown below:

import luigi

class StaticTask(luigi.Task):
    def run(self):
        payload = {'foo': 'bar'}
        with self.output().open('w') as fp:
            json.dump(payload, fp)

    def output(self):
        return luigi.s3.S3Target(s3://foo/bar/baz.txt)

This is fine, but then you either need to mock the S3Target, or create a new class that inherits from StaticTask, and overrides the output with a MockTarget within your unit tests or during runs in local development. Another direction could be to add a luigi parameter to the task, and add logic to the output to select from a list of expected targets, but this still isn’t quite as flexible as one might like.

The OpenerTarget attempts to help alleviate this limitation. The example below allow shows the pattern used it most luigi tasks, but allows the task to be run against the local file system, mock file system, s3 file system, and many others including registration of custom target types.

import luigi

from luigi.contrib.opener import OpenerTarget

class ConfigurableTask(luigi.Task):
    output_file = luigi.parameter(default='s3://foo/bar/baz.txt')

    def run(self):
        payload = {'foo': 'bar'}
        with self.output().open('w') as fp:
            json.dump(payload, fp)

    def output(self):
        return OpenerTarget(self.output_file)

With this pattern, the task can be reconfigured by simply setting the parameter to a different target supported by the opener registry.