Subgroup: Processing

Class: QgsProcessingAlgorithm

class qgis.core.QgsProcessingAlgorithm

Bases: sip.wrapper

Constructor for QgsProcessingAlgorithm.

initAlgorithm() should be called after creating an algorithm to ensure it can correctly configure its parameterDefinitions() and outputDefinitions(). Alternatively, calling create() will return a pre-initialized copy of the algorithm.

Abstract base class for processing algorithms.

New in version 3.0: Methods

addOutput Adds an output definition to the algorithm.
addParameter Adds a parameter definition to the algorithm.
asPythonCommand Returns a Python command string which can be executed to run the algorithm using the specified parameters.
canExecute Returns true if the algorithm can execute.
checkParameterValues Checks the supplied parameter values to verify that they satisfy the requirements of this algorithm in the supplied context.
countVisibleParameters Returns the number of visible (non-hidden) parameters defined by this algorithm.
create Creates a copy of the algorithm, ready for execution.
createCustomParametersWidget If an algorithm subclass implements a custom parameters widget, a copy of this widget should be constructed and returned by this method.
createExpressionContext Creates an expression context relating to the algorithm.
createInstance Creates a new instance of the algorithm class.
destinationParameterDefinitions Returns a list of destination parameters definitions utilized by the algorithm.
displayName Returns the translated algorithm name, which should be used for any user-visible display of the algorithm name.
flags Returns the flags indicating how and when the algorithm operates and should be exposed to users.
group Returns the name of the group this algorithm belongs to.
groupId Returns the unique ID of the group this algorithm belongs to.
hasHtmlOutputs Returns true if this algorithm generates HTML outputs.
helpString Returns a localised help string for the algorithm.
helpUrl Returns a url pointing to the algorithm’s help page.
icon Returns an icon for the algorithm.
id Returns the unique ID for the algorithm, which is a combination of the algorithm provider’s ID and the algorithms unique name (e.g.
initAlgorithm Initializes the algorithm using the specified configuration.
invalidRasterError Returns a user-friendly string to use as an error when a raster layer input could not be loaded.
invalidSinkError Returns a user-friendly string to use as an error when a sink parameter could not be created.
invalidSourceError Returns a user-friendly string to use as an error when a source parameter could not be loaded.
name Returns the algorithm name, used for identifying the algorithm.
outputDefinition Returns a matching output by name.
outputDefinitions Returns an ordered list of output definitions utilized by the algorithm.
parameterAsBool Evaluates the parameter with matching name to a static boolean value.
parameterAsCompatibleSourceLayerPath Evaluates the parameter with matching name to a source vector layer file path of compatible format.
parameterAsCrs Evaluates the parameter with matching name to a coordinate reference system.
parameterAsDouble Evaluates the parameter with matching name to a static double value.
parameterAsEnum Evaluates the parameter with matching name to a enum value.
parameterAsEnums Evaluates the parameter with matching name to list of enum values.
parameterAsExpression Evaluates the parameter with matching name to an expression.
parameterAsExtent Evaluates the parameter with matching name to a rectangular extent.
parameterAsExtentCrs Returns the coordinate reference system associated with an extent parameter value.
parameterAsExtentGeometry Evaluates the parameter with matching name to a rectangular extent, and returns a geometry covering this extent.
parameterAsFields Evaluates the parameter with matching name to a list of fields.
parameterAsFile Evaluates the parameter with matching name to a file/folder name.
parameterAsFileOutput Evaluates the parameter with matching name to a file based output destination.
parameterAsInt Evaluates the parameter with matching name to a static integer value.
parameterAsInts Evaluates the parameter with matching name to a list of integer values.
parameterAsLayer Evaluates the parameter with matching name to a map layer.
parameterAsLayerList Evaluates the parameter with matching name to a list of map layers.
parameterAsMatrix Evaluates the parameter with matching name to a matrix/table of values.
parameterAsOutputLayer Evaluates the parameter with matching name to a output layer destination.
parameterAsPoint Evaluates the parameter with matching name to a point.
parameterAsPointCrs Returns the coordinate reference system associated with an point parameter value.
parameterAsRange Evaluates the parameter with matching name to a range of values.
parameterAsRasterLayer Evaluates the parameter with matching name to a raster layer.
parameterAsSink Evaluates the parameter with matching name to a feature sink.
parameterAsSource Evaluates the parameter with matching name to a feature source.
parameterAsString Evaluates the parameter with matching name to a static string value.
parameterAsVectorLayer Evaluates the parameter with matching name to a vector layer.
parameterDefinition Returns a matching parameter by name.
parameterDefinitions Returns an ordered list of parameter definitions utilized by the algorithm.
postProcess Should be called in the main thread following the completion of runPrepared().
postProcessAlgorithm Allows the algorithm to perform any required cleanup tasks.
prepare Prepares the algorithm for execution.
prepareAlgorithm Prepares the algorithm to run using the specified parameters.
preprocessParameters Pre-processes a set of parameters, allowing the algorithm to clean their values.
processAlgorithm Runs the algorithm using the specified parameters.
provider Returns the provider to which this algorithm belongs.
removeParameter Removes the parameter with matching name from the algorithm, and deletes any existing definition.
run Executes the algorithm using the specified parameters.
runPrepared Runs the algorithm, which has been prepared by an earlier call to prepare().
setProvider Associates this algorithm with its provider.
shortDescription Returns an optional translated short description of the algorithm.
shortHelpString Returns a localised short helper string for the algorithm.
supportInPlaceEdit Checks whether this algorithm supports in-place editing on the given layer Default implementation returns false.
svgIconPath Returns a path to an SVG version of the algorithm’s icon.
tags Returns a list of tags which relate to the algorithm, and are used to assist users in searching for suitable algorithms.
validateInputCrs Checks whether the coordinate reference systems for the specified set of parameters are valid for the algorithm.

Signals

Attributes

FlagCanCancel
FlagDeprecated
FlagDisplayNameIsLiteral
FlagHideFromModeler
FlagHideFromToolbox
FlagNoThreading
FlagRequiresMatchingCrs
FlagSupportsBatch
FlagSupportsInPlaceEdits
class Flag

Bases: int

FlagCanCancel = 16
FlagDeprecated = 6
FlagDisplayNameIsLiteral = 128
FlagHideFromModeler = 4
FlagHideFromToolbox = 2
FlagNoThreading = 64
FlagRequiresMatchingCrs = 32
FlagSupportsBatch = 8
FlagSupportsInPlaceEdits = 256
class Flags

Bases: sip.wrapper

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

addOutput(self, outputDefinition: QgsProcessingOutputDefinition) → bool

Adds an output definition to the algorithm. Ownership of the definition is transferred to the algorithm. Returns true if the output could be successfully added, or false if the output could not be added (e.g. as a result of a duplicate name).

This should usually be called from a subclass’ initAlgorithm() implementation.

Note that in some cases output creation can be automatically performed when calling addParameter(). See the notes in addParameter() for a description of when this occurs.

See also

addParameter()

See also

initAlgorithm()

addParameter(self, parameterDefinition: QgsProcessingParameterDefinition, createOutput: bool = True) → bool

Adds a parameter definition to the algorithm. Ownership of the definition is transferred to the algorithm. Returns true if parameter could be successfully added, or false if the parameter could not be added (e.g. as a result of a duplicate name).

This should usually be called from a subclass’ initAlgorithm() implementation.

If the createOutput argument is true, then a corresponding output definition will also be created (and added to the algorithm) where appropriate. E.g. when adding a QgsProcessingParameterVectorDestination and createOutput is true, then a QgsProcessingOutputVectorLayer output will be created and added to the algorithm. There is no need to call addOutput() to manually add a corresponding output for this vector. If createOutput is false then this automatic output creation will not occur.

See also

initAlgorithm()

See also

addOutput()

asPythonCommand(self, parameters: Dict[str, Any], context: QgsProcessingContext) → str

Returns a Python command string which can be executed to run the algorithm using the specified parameters.

Algorithms which cannot be run from a Python command should return an empty string.

canExecute(self) → Tuple[bool, str]

Returns true if the algorithm can execute. Algorithm subclasses can return false here to indicate that they are not able to execute, e.g. as a result of unmet external dependencies. If specified, the errorMessage argument will be filled with a localised error message describing why the algorithm cannot execute.

checkParameterValues(self, parameters: Dict[str, Any], context: QgsProcessingContext) → Tuple[bool, str]

Checks the supplied parameter values to verify that they satisfy the requirements of this algorithm in the supplied context. The message parameter will be filled with explanatory text if validation fails. Overridden implementations should also check this base class implementation.

Returns:true if parameters are acceptable for the algorithm.
countVisibleParameters(self) → int

Returns the number of visible (non-hidden) parameters defined by this algorithm.

create(self, configuration: Dict[str, Any] = {}) → QgsProcessingAlgorithm

Creates a copy of the algorithm, ready for execution.

This method returns a new, preinitialized copy of the algorithm, ready for executing.

The configuration argument allows passing of a map of configuration settings to the algorithm, allowing it to dynamically adjust its initialized parameters and outputs according to this configuration. This is generally used only for algorithms in a model, allowing them to adjust their behavior at run time according to some user configuration.

See also

initAlgorithm()

createCustomParametersWidget(self, parent: QWidget = None) → QWidget

If an algorithm subclass implements a custom parameters widget, a copy of this widget should be constructed and returned by this method. The base class implementation returns None, which indicates that an autogenerated parameters widget should be used.

createExpressionContext(self, parameters: Dict[str, Any], context: QgsProcessingContext, source: QgsProcessingFeatureSource = None) → QgsExpressionContext

Creates an expression context relating to the algorithm. This can be called by algorithms to create a new expression context ready for evaluating expressions within the algorithm. Optionally, a source can be specified which will be used to populate the context if it implements the QgsExpressionContextGenerator interface.

createInstance(self) → QgsProcessingAlgorithm

Creates a new instance of the algorithm class.

This method should return a ‘pristine’ instance of the algorithm class.

destinationParameterDefinitions(self) → object

Returns a list of destination parameters definitions utilized by the algorithm.

displayName(self) → str

Returns the translated algorithm name, which should be used for any user-visible display of the algorithm name.

Algorithm display names should be short, e.g. ideally no more than 3 or 4 words. The name should use sentence case (e.g. “Raster layer statistics”, not “Raster Layer Statistics”).

See also

name()

flags(self) → QgsProcessingAlgorithm.Flags

Returns the flags indicating how and when the algorithm operates and should be exposed to users. Default flags are FlagSupportsBatch and FlagCanCancel.

group(self) → str

Returns the name of the group this algorithm belongs to. This string should be localised.

See also

groupId()

See also

tags()

groupId(self) → str

Returns the unique ID of the group this algorithm belongs to. This string should be fixed for the algorithm, and must not be localised. The group id should be unique within each provider. Group id should contain lowercase alphanumeric characters only and no spaces or other formatting characters.

See also

group()

hasHtmlOutputs(self) → bool

Returns true if this algorithm generates HTML outputs.

helpString(self) → str

Returns a localised help string for the algorithm. Algorithm subclasses should implement either helpString() or helpUrl().

See also

helpUrl()

Deprecated since version Unused,: will be removed in QGIS 4.0

helpUrl(self) → str

Returns a url pointing to the algorithm’s help page.

See also

helpString()

icon(self) → QIcon

Returns an icon for the algorithm.

See also

svgIconPath()

id(self) → str

Returns the unique ID for the algorithm, which is a combination of the algorithm provider’s ID and the algorithms unique name (e.g. “qgis:mergelayers” ).

See also

name()

See also

provider()

initAlgorithm(self, configuration: Dict[str, Any] = {})

Initializes the algorithm using the specified configuration.

This should be called directly after creating algorithms and before retrieving any parameterDefinitions() or outputDefinitions().

Subclasses should use their implementations to add all required input parameter and output definitions (which can be dynamically adjusted according to configuration).

Dynamic configuration can be used by algorithms which alter their behavior when used inside processing models. For instance, a “feature router” type algorithm which sends input features to one of any number of outputs sinks based on some preconfigured filter parameters can use the init method to create these outputs based on the specified configuration.

See also

addParameter()

See also

addOutput()

invalidRasterError(parameters: Dict[str, Any], name: str) → str

Returns a user-friendly string to use as an error when a raster layer input could not be loaded.

The parameters argument should give the algorithms parameter map, and the name should correspond to the invalid source parameter name.

New in version 3.2.

invalidSinkError(parameters: Dict[str, Any], name: str) → str

Returns a user-friendly string to use as an error when a sink parameter could not be created.

The parameters argument should give the algorithms parameter map, and the name should correspond to the invalid source parameter name.

New in version 3.2.

invalidSourceError(parameters: Dict[str, Any], name: str) → str

Returns a user-friendly string to use as an error when a source parameter could not be loaded.

The parameters argument should give the algorithms parameter map, and the name should correspond to the invalid source parameter name.

New in version 3.2.

name(self) → str

Returns the algorithm name, used for identifying the algorithm. This string should be fixed for the algorithm, and must not be localised. The name should be unique within each provider. Names should contain lowercase alphanumeric characters only and no spaces or other formatting characters.

See also

displayName()

See also

group()

See also

tags()

outputDefinition(self, name: str) → QgsProcessingOutputDefinition

Returns a matching output by name. Matching is done in a case-insensitive manner.

outputDefinitions(self) → object

Returns an ordered list of output definitions utilized by the algorithm.

See also

addOutput()

parameterAsBool(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → bool

Evaluates the parameter with matching name to a static boolean value.

parameterAsCompatibleSourceLayerPath(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext, compatibleFormats: Iterable[str], preferredFormat: str = '', feedback: QgsProcessingFeedback = None) → str

Evaluates the parameter with matching name to a source vector layer file path of compatible format.

If the parameter is evaluated to an existing layer, and that layer is not of the format listed in the compatibleFormats argument, then the layer will first be exported to a compatible format in a temporary location. The function will then return the path to that temporary file.

compatibleFormats should consist entirely of lowercase file extensions, e.g. ‘shp’.

The preferredFormat argument is used to specify to desired file extension to use when a temporary layer export is required.

parameterAsCrs(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsCoordinateReferenceSystem

Evaluates the parameter with matching name to a coordinate reference system.

parameterAsDouble(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → float

Evaluates the parameter with matching name to a static double value.

parameterAsEnum(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → int

Evaluates the parameter with matching name to a enum value.

parameterAsEnums(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → List[int]

Evaluates the parameter with matching name to list of enum values.

parameterAsExpression(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → str

Evaluates the parameter with matching name to an expression.

parameterAsExtent(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsRectangle

Evaluates the parameter with matching name to a rectangular extent.

If crs is set, and the original coordinate reference system of the parameter can be determined, then the extent will be automatically reprojected so that it is in the specified crs. In this case the extent of the reproject rectangle will be returned.

parameterAsExtentCrs(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsCoordinateReferenceSystem

Returns the coordinate reference system associated with an extent parameter value.

parameterAsExtentGeometry(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsGeometry

Evaluates the parameter with matching name to a rectangular extent, and returns a geometry covering this extent.

If crs is set, and the original coordinate reference system of the parameter can be determined, then the extent will be automatically reprojected so that it is in the specified crs. Unlike parameterAsExtent(), the reprojected rectangle returned by this function will no longer be a rectangle itself (i.e. this method returns the geometry of the actual reprojected rectangle, while parameterAsExtent() returns just the extent of the reprojected rectangle).

parameterAsFields(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → List[str]

Evaluates the parameter with matching name to a list of fields.

parameterAsFile(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → str

Evaluates the parameter with matching name to a file/folder name.

parameterAsFileOutput(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → str

Evaluates the parameter with matching name to a file based output destination.

parameterAsInt(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → int

Evaluates the parameter with matching name to a static integer value.

parameterAsInts(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → List[int]

Evaluates the parameter with matching name to a list of integer values.

New in version 3.4.

parameterAsLayer(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsMapLayer

Evaluates the parameter with matching name to a map layer.

Layers will either be taken from context’s active project, or loaded from external sources and stored temporarily in the context. In either case, callers do not need to handle deletion of the returned layer.

parameterAsLayerList(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → List[QgsMapLayer]

Evaluates the parameter with matching name to a list of map layers.

parameterAsMatrix(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → List[Any]

Evaluates the parameter with matching name to a matrix/table of values. Tables are collapsed to a 1 dimensional list.

parameterAsOutputLayer(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → str

Evaluates the parameter with matching name to a output layer destination.

parameterAsPoint(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsPointXY

Evaluates the parameter with matching name to a point.

If crs is set then the point will be automatically reprojected so that it is in the specified crs.

parameterAsPointCrs(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsCoordinateReferenceSystem

Returns the coordinate reference system associated with an point parameter value.

parameterAsRange(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → List[float]

Evaluates the parameter with matching name to a range of values.

parameterAsRasterLayer(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsRasterLayer

Evaluates the parameter with matching name to a raster layer.

Layers will either be taken from context’s active project, or loaded from external sources and stored temporarily in the context. In either case, callers do not need to handle deletion of the returned layer.

parameterAsSink(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext, fields: QgsFields, geometryType: QgsWkbTypes.Type = QgsWkbTypes.NoGeometry, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem(), sinkFlags: Union[QgsFeatureSink.SinkFlags, QgsFeatureSink.SinkFlag] = 0) → Tuple[QgsFeatureSink, str]

Evaluates the parameter with matching name to a feature sink.

Sinks will either be taken from context’s active project, or created from external providers and stored temporarily in the context.

The fields, geometryType and crs parameters dictate the properties of the resulting feature sink.

The destinationIdentifier argument will be set to a string which can be used to retrieve the layer corresponding to the sink, e.g. via calling QgsProcessingUtils.mapLayerFromString()

This function creates a new object and the caller takes responsibility for deleting the returned object.

parameterAsSource(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsProcessingFeatureSource

Evaluates the parameter with matching name to a feature source.

Sources will either be taken from context’s active project, or loaded from external sources and stored temporarily in the context.

This function creates a new object and the caller takes responsibility for deleting the returned object.

parameterAsString(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → str

Evaluates the parameter with matching name to a static string value.

parameterAsVectorLayer(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsVectorLayer

Evaluates the parameter with matching name to a vector layer.

Layers will either be taken from context’s active project, or loaded from external sources and stored temporarily in the context. In either case, callers do not need to handle deletion of the returned layer.

parameterDefinition(self, name: str) → QgsProcessingParameterDefinition

Returns a matching parameter by name. Matching is done in a case-insensitive manner, but exact case matches will be preferred.

parameterDefinitions(self) → object

Returns an ordered list of parameter definitions utilized by the algorithm.

See also

addParameter()

postProcess(self, context: QgsProcessingContext, feedback: QgsProcessingFeedback) → Dict[str, Any]

Should be called in the main thread following the completion of runPrepared(). This method allows the algorithm to perform any required cleanup tasks. The returned variant map includes the results evaluated by the algorithm.

Note

This method modifies the algorithm instance, so it is not safe to call on algorithms directly retrieved from QgsProcessingRegistry and QgsProcessingProvider. Instead, a copy of the algorithm should be created with clone() and prepare()/runPrepared() called on the copy.

postProcessAlgorithm(self, context: QgsProcessingContext, feedback: QgsProcessingFeedback) → Dict[str, Any]

Allows the algorithm to perform any required cleanup tasks. The returned variant map includes the results evaluated by the algorithm. These may be output layer references, or calculated values such as statistical calculations.

The context argument specifies the context in which the algorithm was run.

Postprocess progress should be reported using the supplied feedback object. Additionally, well-behaved algorithms should periodically check feedback to determine whether the post processing should be canceled and exited early.

postProcessAlgorithm should be used to handle any thread-sensitive cleanup which is required by the algorithm. It will always be called from the same thread that context has thread affinity with. While this will generally be the main thread, it is not guaranteed. For instance, algorithms which are run as a step in a larger model or as a subcomponent of a script-based algorithm will call postProcessAlgorithm from the same thread as that model/script it being executed in.

postProcessAlgorithm will not be called if the prepareAlgorithm() step failed (returned false), or if an exception was raised by the processAlgorithm() step.

Returns:A map of algorithm outputs. These may be output layer references, or calculated values such as statistical calculations. Implementations which return a non-empty map will override any results returned by processAlgorithm().
prepare(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback) → bool

Prepares the algorithm for execution. This must be run in the main thread, and allows the algorithm to pre-evaluate input parameters in a thread-safe manner. This must be called before calling runPrepared() (which is safe to do in any thread).

See also

runPrepared()

See also

postProcess()

Note

This method modifies the algorithm instance, so it is not safe to call on algorithms directly retrieved from QgsProcessingRegistry and QgsProcessingProvider. Instead, a copy of the algorithm should be created with clone() and prepare()/runPrepared() called on the copy.

prepareAlgorithm(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback) → bool

Prepares the algorithm to run using the specified parameters. Algorithms should implement their logic for evaluating parameter values here. The evaluated parameter results should be stored in member variables ready for a call to processAlgorithm().

The context argument specifies the context in which the algorithm is being run.

prepareAlgorithm should be used to handle any thread-sensitive preparation which is required by the algorithm. It will always be called from the same thread that context has thread affinity with. While this will generally be the main thread, it is not guaranteed. For instance, algorithms which are run as a step in a larger model or as a subcomponent of a script-based algorithm will call prepareAlgorithm from the same thread as that model/script it being executed in.

Note that the processAlgorithm step uses a temporary context with affinity for the thread in which the algorithm is executed, making it safe for processAlgorithm implementations to load sources and sinks without issue. Implementing prepareAlgorithm is only required if special thread safe handling is required by the algorithm.

Algorithm preparation progress should be reported using the supplied feedback object. Additionally, well-behaved algorithms should periodically check feedback to determine whether the algorithm should be canceled and exited early.

If the preparation was successful algorithms must return true. If a false value is returned this indicates that the preparation could not be completed, and the algorithm execution will be canceled.

Returns:true if preparation was successful.
preprocessParameters(self, parameters: Dict[str, Any]) → Dict[str, Any]

Pre-processes a set of parameters, allowing the algorithm to clean their values.

This method is automatically called after users enter parameters, e.g. via the algorithm dialog. This method should NOT be called manually by algorithms.

processAlgorithm(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback) → Dict[str, Any]

Runs the algorithm using the specified parameters. Algorithms should implement their custom processing logic here.

The context argument gives a temporary context with thread affinity matching the thread in which the algorithm is being run. This is a cut-back copy of the context passed to the prepareAlgorithm() and postProcessAlgorithm() steps, but it is generally safe for most algorithms to utilize this context for loading layers and creating sinks. Any loaded layers or sinks created within this temporary context will be transferred back to the main execution context upon successful completion of the processAlgorithm() step.

Algorithm progress should be reported using the supplied feedback object. Additionally, well-behaved algorithms should periodically check feedback to determine whether the algorithm should be canceled and exited early.

This method will not be called if the prepareAlgorithm() step failed (returned false).

c++ implementations of processAlgorithm can throw the QgsProcessingException exception to indicate that a fatal error occurred within the execution. Python based subclasses should raise GeoAlgorithmExecutionException for the same purpose.

Returns:A map of algorithm outputs. These may be output layer references, or calculated values such as statistical calculations. Unless the algorithm subclass overrides the postProcessAlgorithm() step this returned map will be used as the output for the algorithm.
provider(self) → QgsProcessingProvider

Returns the provider to which this algorithm belongs.

removeParameter(self, name: str)

Removes the parameter with matching name from the algorithm, and deletes any existing definition.

run(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback, configuration: Dict[str, Any] = {}) → Tuple[Dict[str, Any], bool]

Executes the algorithm using the specified parameters. This method internally creates a copy of the algorithm before running it, so it is safe to call on algorithms directly retrieved from QgsProcessingRegistry and QgsProcessingProvider.

The context argument specifies the context in which the algorithm is being run.

Algorithm progress should be reported using the supplied feedback object.

If specified, ok will be set to true if algorithm was successfully run.

Returns:A map of algorithm outputs. These may be output layer references, or calculated values such as statistical calculations.

Note

this method can only be called from the main thread. Use prepare(), runPrepared() and postProcess() if you need to run algorithms from a background thread, or use the QgsProcessingAlgRunnerTask class.

runPrepared(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback) → Dict[str, Any]

Runs the algorithm, which has been prepared by an earlier call to prepare(). This method is safe to call from any thread. Returns true if the algorithm was successfully executed. After runPrepared() has finished, the postProcess() method should be called from the main thread to allow the algorithm to perform any required cleanup tasks and return its final result.

See also

prepare()

See also

postProcess()

Note

This method modifies the algorithm instance, so it is not safe to call on algorithms directly retrieved from QgsProcessingRegistry and QgsProcessingProvider. Instead, a copy of the algorithm should be created with clone() and prepare()/runPrepared() called on the copy.

setProvider(self, provider: QgsProcessingProvider)

Associates this algorithm with its provider. No transfer of ownership is involved.

shortDescription(self) → str

Returns an optional translated short description of the algorithm. This should be at most a single sentence, e.g. “Converts 2D features to 3D by sampling a DEM raster.”

New in version 3.2.

shortHelpString(self) → str

Returns a localised short helper string for the algorithm. This string should provide a basic description about what the algorithm does and the parameters and outputs associated with it.

See also

helpString()

See also

helpUrl()

supportInPlaceEdit(self, layer: QgsMapLayer) → bool

Checks whether this algorithm supports in-place editing on the given layer Default implementation returns false.

Returns:true if the algorithm supports in-place editing

New in version 3.4.

svgIconPath(self) → str

Returns a path to an SVG version of the algorithm’s icon.

See also

icon()

tags(self) → List[str]

Returns a list of tags which relate to the algorithm, and are used to assist users in searching for suitable algorithms. These tags should be localised.

validateInputCrs(self, parameters: Dict[str, Any], context: QgsProcessingContext) → bool

Checks whether the coordinate reference systems for the specified set of parameters are valid for the algorithm. For instance, the base implementation performs checks to ensure that all input CRS are equal Returns true if parameters have passed the CRS check.