taskFactory.py

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# This file is part of pipe_base.
#
# Developed for the LSST Data Management System.
# This product includes software developed by the LSST Project
# (http://www.lsst.org).
# See the COPYRIGHT file at the top-level directory of this distribution
# for details of code ownership.
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# This program is free software: you can redistribute it and/or modify
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"""Module defining TaskFactory interface.
"""

__all__ = ["TaskFactory"]

from abc import ABCMeta, abstractmethod


class TaskFactory(metaclass=ABCMeta):
    """Abstract base class for task factory.

    Task factory is responsible for importing PipelineTask subclasses by
    name and creating instances of these classes.
    """

    @abstractmethod
    def loadTaskClass(self, taskName):
        """Locate and import PipelineTask class.

        Returns tuple of task class and its full name, `None` is returned
        for both if loading fails.

        Parameters
        ----------
        taskName : `str`
            Name of the PipelineTask class, interpretation depends entirely on
            activator, e.g. it may or may not include dots.

        Returns
        -------
        taskClass : `type`
            PipelineTask class object, or None on failure.
        taskName : `str`
            Full task class name including package and module, or None on
            failure.

        Raises
        ------
        ImportError
            Raised if task class cannot be imported.
        TypeError
            Raised if imported class is not a PipelineTask.
        """

    @abstractmethod
    def makeTask(self, taskClass, config, overrides, butler):
        """Create new PipelineTask instance from its class.

        Parameters
        ----------
        taskClass : `type`
            `PipelineTask` sub-class.
        config : `pex.Config` or `None`
            Configuration object, if `None` then use task-defined
            configuration class (``taskClass.ConfigClass``) to create new
            instance.
        overrides : `ConfigOverrides` or `None`
            Configuration overrides, this should contain all overrides to be
            applied to a default task config, including instrument-specific,
            obs-package specific, and possibly command-line overrides. This
            parameter is exclusive with ``config``, only one of the two can be
            specified as not-`None`.
        butler : `~lsst.daf.butler.Butler` or None
            Butler instance used to obtain initialization inputs for
            PipelineTasks. If `None`, some PipelineTasks will not be usable

        Returns
        -------
        task : `PipelineTask`
            Instance of a `PipelineTask` class or `None` on errors.

        Raises
        ------
        Any exceptions that are raised by PipelineTask constructor or its
        configuration class are propagated back to caller.
        """