Subgroup: Processing

Class: QgsProcessingContext

class qgis.core.QgsProcessingContext

Bases: sip.wrapper

Constructor for QgsProcessingContext.

Contains information about the context in which a processing algorithm is executed.

Contextual information includes settings such as the associated project, and expression context.

New in version 3.0: Methods

addLayerToLoadOnCompletion Adds a layer to load (by ID or datasource) into the canvas upon completion of the algorithm or model.
copyThreadSafeSettings Copies all settings which are safe for use across different threads from other to this context.
defaultEncoding Returns the default encoding to use for newly created files.
expressionContext Returns the expression context.
feedback Returns the associated feedback object.
flags Returns any flags set in the context.
getMapLayer Returns a map layer from the context with a matching identifier.
invalidGeometryCheck Returns the behavior used for checking invalid geometries in input layers.
layerToLoadOnCompletionDetails Returns a reference to the details for a given layer which is loaded on completion of the algorithm or model.
layersToLoadOnCompletion Returns a map of layers (by ID or datasource) to LayerDetails, to load into the canvas upon completion of the algorithm or model.
project Returns the project in which the algorithm is being executed.
pushToThread Pushes the thread affinity for the context (including all layers contained in the temporaryLayerStore()) into another thread.
setDefaultEncoding Sets the default encoding to use for newly created files.
setExpressionContext Sets the expression context.
setFeedback Sets an associated feedback object.
setFlags Sets flags for the context.
setInvalidGeometryCallback Sets a callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid.
setInvalidGeometryCheck Sets the behavior used for checking invalid geometries in input layers.
setLayersToLoadOnCompletion Sets the map of layers (by ID or datasource) to LayerDetails, to load into the canvas upon completion of the algorithm or model.
setProject Sets the project in which the algorithm will be executed.
setTransformContext Sets the coordinate transform context.
setTransformErrorCallback Sets a callback function to use when encountering a transform error when iterating features.
takeResultLayer Takes the result map layer with matching id from the context and transfers ownership of it back to the caller.
takeResultsFrom Takes the results from another context and merges them with the results currently stored in this context.
temporaryLayerStore Returns a reference to the layer store used for storing temporary layers during algorithm execution.
thread Returns the thread in which the context lives.
transformContext Returns the coordinate transform context.
willLoadLayerOnCompletion Returns true if the given layer (by ID or datasource) will be loaded into the current project upon completion of the algorithm or model.

Signals

Attributes

class Flag

Bases: int

class Flags

Bases: sip.wrapper

QgsProcessingContext.Flags(Union[QgsProcessingContext.Flags, QgsProcessingContext.Flag]) QgsProcessingContext.Flags(QgsProcessingContext.Flags)

class LayerDetails(name: str, project: QgsProject, outputName: str = '')

Bases: sip.wrapper

Constructor for LayerDetails.

QgsProcessingContext.LayerDetails() Default constructor

QgsProcessingContext.LayerDetails(QgsProcessingContext.LayerDetails)

Details for layers to load into projects.

New in version 3.0.

name
outputName
postProcessor(self) → QgsProcessingLayerPostProcessorInterface

Layer post-processor. May be None if no post-processing is required.

New in version 3.2.

project
setPostProcessor(self, processor: QgsProcessingLayerPostProcessorInterface)

Sets the layer post-processor. May be None if no post-processing is required.

Ownership of processor is transferred.

New in version 3.2.

See also

postProcessor()

addLayerToLoadOnCompletion(self, layer: str, details: QgsProcessingContext.LayerDetails)

Adds a layer to load (by ID or datasource) into the canvas upon completion of the algorithm or model. The details parameter dictates the LayerDetails.

copyThreadSafeSettings(self, other: QgsProcessingContext)

Copies all settings which are safe for use across different threads from other to this context.

defaultEncoding(self) → str

Returns the default encoding to use for newly created files.

expressionContext(self) → QgsExpressionContext

Returns the expression context.

feedback(self) → QgsProcessingFeedback

Returns the associated feedback object.

See also

setFeedback()

flags(self) → QgsProcessingContext.Flags

Returns any flags set in the context.

See also

setFlags()

getMapLayer(self, identifier: str) → QgsMapLayer

Returns a map layer from the context with a matching identifier. This method considers layer IDs, names and sources when matching the identifier (see QgsProcessingUtils.mapLayerFromString() for details).

Ownership is not transferred and remains with the context.

invalidGeometryCheck(self) → QgsFeatureRequest.InvalidGeometryCheck

Returns the behavior used for checking invalid geometries in input layers.

layerToLoadOnCompletionDetails(self, layer: str) → QgsProcessingContext.LayerDetails

Returns a reference to the details for a given layer which is loaded on completion of the algorithm or model.

Warning

First check willLoadLayerOnCompletion(), or calling this method will incorrectly add layer as a layer to load on completion.

New in version 3.2.

layersToLoadOnCompletion(self) → object

Returns a map of layers (by ID or datasource) to LayerDetails, to load into the canvas upon completion of the algorithm or model.

project(self) → QgsProject

Returns the project in which the algorithm is being executed.

See also

setProject()

pushToThread(self, thread: QThread)

Pushes the thread affinity for the context (including all layers contained in the temporaryLayerStore()) into another thread. This method is only safe to call when the current thread matches the existing thread affinity for the context (see thread()).

See also

thread()

setDefaultEncoding(self, encoding: str)

Sets the default encoding to use for newly created files.

setExpressionContext(self, context: QgsExpressionContext)

Sets the expression context.

setFeedback(self, feedback: QgsProcessingFeedback)

Sets an associated feedback object. This allows context related functions to report feedback and errors to users and processing logs. While ideally this feedback object should outlive the context, only a weak pointer to feedback is stored and no errors will occur if feedback is deleted before the context. Ownership of feedback is not transferred.

See also

setFeedback()

setFlags(self, flags: Union[QgsProcessingContext.Flags, QgsProcessingContext.Flag])

Sets flags for the context.

See also

flags()

setInvalidGeometryCallback(self, Callable[..., None])

Sets a callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid. This function will be called using the feature with invalid geometry as a parameter.

New in version 3.0.

See also

invalidGeometryCallback()

setInvalidGeometryCheck(self, check: QgsFeatureRequest.InvalidGeometryCheck)

Sets the behavior used for checking invalid geometries in input layers. Settings this to anything but QgsFeatureRequest.GeometryNoCheck will also reset the invalidGeometryCallback() to a default implementation.

setLayersToLoadOnCompletion(self, layers: Dict[str, QgsProcessingContext.LayerDetails])

Sets the map of layers (by ID or datasource) to LayerDetails, to load into the canvas upon completion of the algorithm or model.

setProject(self, project: QgsProject)

Sets the project in which the algorithm will be executed.

This also automatically sets the transformContext() to match the project’s transform context.

See also

project()

setTransformContext(self, context: QgsCoordinateTransformContext)

Sets the coordinate transform context.

Note that setting a project for the context will automatically set the coordinate transform context.

setTransformErrorCallback(self, Callable[..., None])

Sets a callback function to use when encountering a transform error when iterating features. This function will be called using the feature which encountered the transform error as a parameter.

New in version 3.0.

See also

transformErrorCallback()

takeResultLayer(self, id: str) → QgsMapLayer

Takes the result map layer with matching id from the context and transfers ownership of it back to the caller. This method can be used to remove temporary layers which are not required for further processing from a context.

See also

getMapLayer()

takeResultsFrom(self, context: QgsProcessingContext)

Takes the results from another context and merges them with the results currently stored in this context. This includes settings like any layers loaded in the temporaryLayerStore() and layersToLoadOnCompletion(). This is only safe to call when both this context and the other context share the same thread() affinity, and that thread is the current thread.

temporaryLayerStore(self) → QgsMapLayerStore

Returns a reference to the layer store used for storing temporary layers during algorithm execution.

thread(self) → QThread

Returns the thread in which the context lives.

See also

pushToThread()

transformContext(self) → QgsCoordinateTransformContext

Returns the coordinate transform context.

willLoadLayerOnCompletion(self, layer: str) → bool

Returns true if the given layer (by ID or datasource) will be loaded into the current project upon completion of the algorithm or model.

New in version 3.2.