Task

class lsst.pipe.base.Task(config=None, name=None, parentTask=None, log=None)

Bases: object

Base class for data processing tasks.

See Overview of the task framework to learn what tasks are, and Creating a task for more information about writing tasks.

Parameters:

config : Task.ConfigClass instance, optional

Configuration for this task (an instance of Task.ConfigClass, which is a task-specific subclass of lsst.pex.config.Config, or None. If None:

• If parentTask specified then defaults to parentTask.config.<name>
• If parentTask is None then defaults to self.ConfigClass()

name : str, optional

Brief name of task, or None; if None then defaults to Task._DefaultName

parentTask : Task-type, optional

The parent task of this subtask, if any.

• If None (a top-level task) then you must specify config and name is ignored.
• If not None (a subtask) then you must specify name.

log : lsst.log.Log, optional

Log whose name is used as a log name prefix, or None for no prefix. Ignored if is parentTask specified, in which case parentTask.log‘s name is used as a prefix. The task’s log name is prefix + "." + name if a prefix exists, else name. The task’s log is then a child logger of parentTask.log (if parentTask specified), or a child logger of the log from the argument (if log is not None).

Raises:

RuntimeError

Raised under these circumstances:

• If parentTask is None and config is None.
• If parentTask is not None and name is None.
• If name is None and _DefaultName does not exist.

Notes

Useful attributes include:

• log: an lsst.log.Log
• config: task-specific configuration; an instance of ConfigClass (see below).

• metadata: an lsst.daf.base.PropertyList for collecting task-specific metadata,

  e.g. data quality and performance metrics. This is data that is only meant to be persisted, never to be used by the task.

Subclasses typically have a method named run to perform the main data processing. Details:

• run should process the minimum reasonable amount of data, typically a single CCD. Iteration, if desired, is performed by a caller of the run method. This is good design and allows multiprocessing without the run method having to support it directly.
• If run can persist or unpersist data:
  • run should accept a butler data reference (or a collection of data references, if appropriate, e.g. coaddition).
  • There should be a way to run the task without persisting data. Typically the run method returns all data, even if it is persisted, and the task’s config method offers a flag to disable persistence.

Deprecated: Tasks other than cmdLineTask.CmdLineTask%s should not accept a blob such as a butler data reference. How we will handle data references is still TBD, so don’t make changes yet! RHL 2014-06-27

Subclasses must also have an attribute ConfigClass that is a subclass of lsst.pex.config.Config which configures the task. Subclasses should also have an attribute _DefaultName: the default name if there is no parent task. _DefaultName is required for subclasses of CmdLineTask and recommended for subclasses of Task because it simplifies construction (e.g. for unit tests).

Tasks intended to be run from the command line should be subclasses of CmdLineTask not Task.

Methods Summary

emptyMetadata()	Empty (clear) the metadata for this Task and all sub-Tasks.
getAllSchemaCatalogs()	Get schema catalogs for all tasks in the hierarchy, combining the results into a single dict.
getFullMetadata()	Get metadata for all tasks.
getFullName()	Get the task name as a hierarchical name including parent task names.
getName()	Get the name of the task.
getSchemaCatalogs()	Get the schemas generated by this task.
getTaskDict()	Get a dictionary of all tasks as a shallow copy.
makeField(doc)	Make a lsst.pex.config.ConfigurableField for this task.
makeSubtask(name, **keyArgs)	Create a subtask as a new instance as the name attribute of this task.
timer(name[, logLevel])	Context manager to log performance data for an arbitrary block of code.

Methods Documentation

emptyMetadata()

Empty (clear) the metadata for this Task and all sub-Tasks.

getAllSchemaCatalogs()

Get schema catalogs for all tasks in the hierarchy, combining the results into a single dict.

Returns:

schemacatalogs : dict

Keys are butler dataset type, values are a empty catalog (an instance of the appropriate lsst.afw.table Catalog type) for all tasks in the hierarchy, from the top-level task down through all subtasks.

Notes

This method may be called on any task in the hierarchy; it will return the same answer, regardless.

The default implementation should always suffice. If your subtask uses schemas the override Task.getSchemaCatalogs, not this method.

getFullMetadata()

Get metadata for all tasks.

Returns:

metadata : lsst.daf.base.PropertySet

The PropertySet keys are the full task name. Values are metadata for the top-level task and all subtasks, sub-subtasks, etc..

Notes

The returned metadata includes timing information (if @timer.timeMethod is used) and any metadata set by the task. The name of each item consists of the full task name with . replaced by :, followed by . and the name of the item, e.g.:

topLevelTaskName:subtaskName:subsubtaskName.itemName

using : in the full task name disambiguates the rare situation that a task has a subtask and a metadata item with the same name.

getFullName()

Get the task name as a hierarchical name including parent task names.

Returns:

fullName : str

The full name consists of the name of the parent task and each subtask separated by periods. For example:

• The full name of top-level task “top” is simply “top”.
• The full name of subtask “sub” of top-level task “top” is “top.sub”.
• The full name of subtask “sub2” of subtask “sub” of top-level task “top” is “top.sub.sub2”.

getName()

Get the name of the task.

Returns:

taskName : str

Name of the task.

See also

getFullName

getSchemaCatalogs()

Get the schemas generated by this task.

Returns:

schemaCatalogs : dict

Keys are butler dataset type, values are an empty catalog (an instance of the appropriate lsst.afw.table Catalog type) for this task.

See also

Task.getAllSchemaCatalogs

Notes

Warning

Subclasses that use schemas must override this method. The default implemenation returns an empty dict.

This method may be called at any time after the Task is constructed, which means that all task schemas should be computed at construction time, not when data is actually processed. This reflects the philosophy that the schema should not depend on the data.

Returning catalogs rather than just schemas allows us to save e.g. slots for SourceCatalog as well.

getTaskDict()

Get a dictionary of all tasks as a shallow copy.

Returns:

taskDict : dict

Dictionary containing full task name: task object for the top-level task and all subtasks, sub-subtasks, etc..

classmethod makeField(doc)

Make a lsst.pex.config.ConfigurableField for this task.

Parameters:

doc : str

Help text for the field.

Returns:

configurableField : lsst.pex.config.ConfigurableField

A ConfigurableField for this task.

Examples

Provides a convenient way to specify this task is a subtask of another task.

Here is an example of use:

class OtherTaskConfig(lsst.pex.config.Config)
    aSubtask = ATaskClass.makeField("a brief description of what this task does")

makeSubtask(name, **keyArgs)

Create a subtask as a new instance as the name attribute of this task.

Parameters:

name : str

Brief name of the subtask.

keyArgs

Extra keyword arguments used to construct the task. The following arguments are automatically provided and cannot be overridden:

• “config”.
• “parentTask”.

Notes

The subtask must be defined by Task.config.name, an instance of pex_config ConfigurableField or RegistryField.

timer(name, logLevel=10000)

Context manager to log performance data for an arbitrary block of code.

Parameters:

name : str

Name of code being timed; data will be logged using item name: Start and End.

logLevel

A lsst.log level constant.

See also

timer.logInfo

Examples

Creating a timer context:

with self.timer("someCodeToTime"):
    pass  # code to time