Class: QgsProcessingAlgorithm¶

Abstract base class for processing algorithms.

Note

This is an abstract class, with methods which must be implemented by a subclass.

The following methods must be implemented: createInstance(), displayName(), initAlgorithm(), name(), processAlgorithm()

Class Hierarchy¶

Subclasses¶

`QgsProcessingFeatureBasedAlgorithm`	An abstract `QgsProcessingAlgorithm` base class for processing algorithms which operate “feature-by-feature”.
`QgsProcessingModelAlgorithm`	Model based algorithm with processing.

Enums

`Flag`	alias of `ProcessingAlgorithmFlag`
`PropertyAvailability`	alias of `ProcessingPropertyAvailability`

Abstract Methods

`createInstance`	Creates a new instance of the algorithm class.
`displayName`	Returns the translated algorithm name, which should be used for any user-visible display of the algorithm name.
`initAlgorithm`	Initializes the algorithm using the specified configuration.
`name`	Returns the algorithm name, used for identifying the algorithm.
`processAlgorithm`	Runs the algorithm using the specified parameters.

Methods

`addOutput`	Adds an output definition to the algorithm.
`addParameter`	Adds a parameter definition to the algorithm.
`countVisibleParameters`	Returns the number of visible (non-hidden) parameters defined by this algorithm.
`create`	Creates a copy of the algorithm, ready for execution.
`destinationParameterDefinitions`	Returns a list of destination parameters definitions utilized by the algorithm.
`hasHtmlOutputs`	Returns `True` if this algorithm generates HTML outputs.
`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. "qgis:mergelayers" ).
`outputDefinition`	Returns a matching output by name.
`outputDefinitions`	Returns an ordered list of output definitions utilized by the algorithm.
`parameterAsAnnotationLayer`	Evaluates the parameter with matching name to an annotation layer.
`parameterAsBool`	Evaluates the parameter with matching name to a static boolean value.
`parameterAsBoolean`	Evaluates the parameter with matching name to a static boolean value.
`parameterAsColor`	Evaluates the parameter with matching name to a color, or returns an invalid color if the parameter was not set.
`parameterAsCompatibleSourceLayerPath`	Evaluates the parameter with matching name to a source vector layer file path of compatible format.
`parameterAsCompatibleSourceLayerPathAndLayerName`	Evaluates the parameter with matching name to a source vector layer file path and layer name of compatible format.
`parameterAsConnectionName`	Evaluates the parameter with matching name to a connection name string.
`parameterAsCrs`	Evaluates the parameter with matching name to a coordinate reference system.
`parameterAsDatabaseTableName`	Evaluates the parameter with matching name to a database table name string.
`parameterAsDateTime`	Evaluates the parameter with matching name to a DateTime, or returns an invalid date time if the parameter was not set.
`parameterAsDouble`	Evaluates the parameter with matching name to a static double value.
`parameterAsEnum`	Evaluates the parameter with matching name to a enum value.
`parameterAsEnumString`	Evaluates the parameter with matching name to a static enum string.
`parameterAsEnumStrings`	Evaluates the parameter with matching name to list of static enum strings.
`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.
`parameterAsFileList`	Evaluates the parameter with matching name to a list of files (for `QgsProcessingParameterMultipleLayers` in `QgsProcessing`:TypeFile mode).
`parameterAsFileOutput`	Evaluates the parameter with matching name to a file based output destination.
`parameterAsGeometry`	Evaluates the parameter with matching name to a geometry.
`parameterAsGeometryCrs`	Returns the coordinate reference system associated with a geometry parameter value.
`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.
`parameterAsLayout`	Evaluates the parameter with matching name to a print layout.
`parameterAsLayoutItem`	Evaluates the parameter with matching name to a print layout item, taken from the specified layout.
`parameterAsMatrix`	Evaluates the parameter with matching name to a matrix/table of values.
`parameterAsMeshLayer`	Evaluates the parameter with matching name to a mesh layer.
`parameterAsOutputLayer`	Evaluates the parameter with matching name to a output layer destination.
`parameterAsPoint`	Evaluates the parameter with matching name to a point.
`parameterAsPointCloudLayer`	Evaluates the parameter with matching name to a point cloud layer.
`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.
`parameterAsSchema`	Evaluates the parameter with matching name to a database schema name string.
`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.
`parameterAsStrings`	Evaluates the parameter with matching name to a list of strings (e.g. field names or point cloud attributes).
`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()`.
`prepare`	Prepares the algorithm for execution.
`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.

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsProcessingAlgorithm. See the FAQ for more details.

`asMap`	Returns a JSON serializable variant map containing the specified parameters and context settings.
`asPythonCommand`	Returns a Python command string which can be executed to run the algorithm using the specified parameters.
`asQgisProcessCommand`	Returns a command string which will execute the algorithm using the specified parameters via the command line qgis_process tool.
`autogenerateParameterValues`	Returns a map of default auto-generated parameters to fill in, based on existing 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.
`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.
`documentationFlags`	Returns the flags describing algorithm behavior for documentation purposes.
`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.
`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.
`postProcessAlgorithm`	Allows the algorithm to perform any required cleanup tasks.
`prepareAlgorithm`	Prepares the algorithm to run using the specified parameters.
`preprocessParameters`	Pre-processes a set of parameters, allowing the algorithm to clean their values.
`shortDescription`	Returns an optional translated short description of the algorithm.
`shortHelpString`	Returns a localised short helper string for the algorithm.
`sinkProperties`	Returns the vector properties which will be used for the sink with matching name.
`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.

Static Methods

`invalidPointCloudError`	Returns a user-friendly string to use as an error when a point cloud layer input could not be loaded.
`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.
`writeFeatureError`	Returns a user-friendly string to use as an error when a feature cannot be written into a sink.

class qgis.core.QgsProcessingAlgorithm[source]¶

Bases: object

__init__()

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.

Flag¶: alias of ProcessingAlgorithmFlag

Flags¶: alias of ProcessingAlgorithmFlags

PropertyAvailability¶: alias of ProcessingPropertyAvailability

class VectorProperties¶

Bases: object

Properties of a vector source or sink used in an algorithm.

Added in version 3.14.

availability: ProcessingPropertyAvailability¶: Availability of the properties. By default properties are not available.

crs: QgsCoordinateReferenceSystem¶: Coordinate Reference System

fields: QgsFields¶: Fields

wkbType: WkbType¶: Geometry (WKB) type

addOutput(self, outputDefinition: QgsProcessingOutputDefinition | None) → bool[source]¶

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()

Parameters:: outputDefinition (Optional[QgsProcessingOutputDefinition])
Return type:: bool

addParameter(self, parameterDefinition: QgsProcessingParameterDefinition | None, createOutput: bool = True) → bool[source]¶

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()

Parameters:

parameterDefinition (Optional[QgsProcessingParameterDefinition])
createOutput (bool = True)

Return type:

bool

virtual asMap(self, parameters: Dict[str, Any], context: QgsProcessingContext) → Dict[str, Any][source]¶

Returns a JSON serializable variant map containing the specified parameters and context settings.

Added in version 3.24.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)

Return type:

Dict[str, Any]

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

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)

Return type:

str

virtual asQgisProcessCommand(self, parameters: Dict[str, Any], context: QgsProcessingContext)[source]¶

Returns a command string which will execute the algorithm using the specified parameters via the command line qgis_process tool.

Note that some combinations of parameter types and values cannot be represented as a qgis_process string.

Parameters:

parameters (Dict[str, Any]) – algorithm parameters
context (QgsProcessingContext) -> (str) – processing context

Returns:

equivalent qgis_process command
ok: True if the command was successfully generated

Added in version 3.24.

virtual autogenerateParameterValues(self, existingParameters: Dict[str, Any], changedParameter: str | None, mode: Qgis.ProcessingMode) → Dict[str, Any][source]¶

Returns a map of default auto-generated parameters to fill in, based on existing parameters.

This method is used to automatically fill parameter values when a row is added or modified in the batch processing interface, or automatically update other parameter values when parameters are modified in the toolbox mode.

Parameters:

existingParameters (Dict[str, Any]) – map of current parameter values
changedParameter (Optional[str]) – name of parameter which has just been changed, triggering the update of default parameter values
mode (Qgis.ProcessingMode) – current Processing mode. Allows different autogenerate behavior for batch mode, modeler or toolbox.

Return type:

Dict[str, Any]

Returns:

map of default parameter values to use for the algorithm. Any matching parameters included in the map will be automatically overridden with the value from the returned map. Parameter names not included in the returned map will remain unchanged.

The default behavior is to return an empty map, indicating that no parameters should be automatically generated.

Added in version 3.44.

virtual canExecute(self)[source]¶: 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.

virtual checkParameterValues(self, parameters: Dict[str, Any], context: QgsProcessingContext)[source]¶

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext) -> (bool)

countVisibleParameters(self) → int[source]¶

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

Return type:: int

create(self, configuration: Dict[str, Any] = {}) → QgsProcessingAlgorithm | None[source]¶

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.

Raises a QgsProcessingException if a new algorithm instance could not be created, e.g. if there is an issue with the subclass’ createInstance() method.

See also

initAlgorithm()

Parameters:: configuration (Dict[str, Any] = {})
Return type:: Optional[QgsProcessingAlgorithm]

virtual createCustomParametersWidget(self, parent: QWidget | None = None) → QWidget | None[source]¶

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.

Parameters:: parent (Optional[QWidget] = None)
Return type:: Optional[QWidget]

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

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)
source (Optional[QgsProcessingFeatureSource] = None)

Return type:

QgsExpressionContext

abstract createInstance(self) → QgsProcessingAlgorithm | None[source]¶

Creates a new instance of the algorithm class.

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

Return type:: Optional[QgsProcessingAlgorithm]

destinationParameterDefinitions(self) → List[QgsProcessingParameterDefinition][source]¶

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

See also

parameterDefinitions()

Return type:: List[QgsProcessingParameterDefinition]

abstract displayName(self) → str[source]¶

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()

See also

shortDescription()

Return type:: str

virtual documentationFlags(self) → Qgis.ProcessingAlgorithmDocumentationFlags[source]¶

Returns the flags describing algorithm behavior for documentation purposes.

The default is to return no flags.

Added in version 3.40.

Return type:: Qgis.ProcessingAlgorithmDocumentationFlags

virtual flags(self) → Qgis.ProcessingAlgorithmFlags[source]¶

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

Return type:: Qgis.ProcessingAlgorithmFlags

virtual group(self) → str[source]¶

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

See also

groupId()

See also

tags()

Return type:: str

virtual groupId(self) → str[source]¶

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()

Return type:: str

hasHtmlOutputs(self) → bool[source]¶

Returns True if this algorithm generates HTML outputs.

Return type:: bool

virtual helpString(self) → str[source]¶

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

See also

helpUrl()

See also

shortHelpString()

Deprecated since version 3.40: Unused, will be removed in QGIS 4.0.

Return type:: str

virtual helpUrl(self) → str[source]¶

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

See also

helpString()

See also

shortHelpString()

Return type:: str

virtual icon(self) → QIcon[source]¶

Returns an icon for the algorithm.

See also

svgIconPath()

Return type:: QIcon

id(self) → str[source]¶

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()

Return type:: str

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

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()

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

static invalidPointCloudError(parameters: Dict[str, Any], name: str | None) → str[source]¶

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

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

See also

invalidSourceError()

See also

invalidSinkError()

See also

invalidRasterError()

Added in version 3.32.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])

Return type:

str

static invalidRasterError(parameters: Dict[str, Any], name: str | None) → str[source]¶

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 raster parameter name.

See also

invalidSourceError()

See also

invalidSinkError()

See also

invalidPointCloudError()

Added in version 3.2.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])

Return type:

str

static invalidSinkError(parameters: Dict[str, Any], name: str | None) → str[source]¶

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 sink parameter name.

See also

invalidSourceError()

See also

invalidRasterError()

See also

invalidPointCloudError()

Added in version 3.2.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])

Return type:

str

static invalidSourceError(parameters: Dict[str, Any], name: str | None) → str[source]¶

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.

See also

invalidRasterError()

See also

invalidSinkError()

See also

invalidPointCloudError()

Added in version 3.2.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])

Return type:

str

abstract name(self) → str[source]¶

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()

Return type:: str

outputDefinition(self, name: str | None) → QgsProcessingOutputDefinition | None[source]¶

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

See also

outputDefinitions()

Parameters:: name (Optional[str])
Return type:: Optional[QgsProcessingOutputDefinition]

outputDefinitions(self) → List[QgsProcessingOutputDefinition][source]¶

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

See also

addOutput()

See also

outputDefinition()

Return type:: List[QgsProcessingOutputDefinition]

parameterAsAnnotationLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsAnnotationLayer | None[source]¶

Evaluates the parameter with matching name to an annotation layer.

Annotation layers will be taken from context’s active project. Callers do not need to handle deletion of the returned layer.

Warning

Working with annotation layers is generally not thread safe (unless the layers are from a QgsProject loaded directly in a background thread). Ensure your algorithm returns the QgsProcessingAlgorithm.FlagNoThreading flag or only accesses annotation layers from a prepareAlgorithm() or postProcessAlgorithm() step.

Added in version 3.22.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsAnnotationLayer]

parameterAsBool(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → bool[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

bool

parameterAsBoolean(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → bool[source]¶

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

Added in version 3.8.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

bool

parameterAsColor(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QColor[source]¶

Evaluates the parameter with matching name to a color, or returns an invalid color if the parameter was not set.

Added in version 3.10.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

QColor

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

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.

When an algorithm is capable of handling multi-layer input files (such as Geopackage), it is preferable to use parameterAsCompatibleSourceLayerPathAndLayerName() which may avoid conversion in more situations.

Parameters:

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

Return type:

str

parameterAsCompatibleSourceLayerPathAndLayerName(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, compatibleFormats: Iterable[str | None], preferredFormat: str | None = '', feedback: QgsProcessingFeedback | None = None)[source]¶

Evaluates the parameter with matching name to a source vector layer file path and layer name 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. This defaults to shapefiles, because shapefiles are the future (don’t believe the geopackage hype!).

This method should be preferred over parameterAsCompatibleSourceLayerPath() when an algorithm is able to correctly handle files with multiple layers. Unlike parameterAsCompatibleSourceLayerPath(), it will not force a conversion in this case and will return the target layer name in the layerName argument.

Parameters:

parameters (Dict[str, Any]) – input parameter value map
name (Optional[str]) – name of target parameter
context (QgsProcessingContext) – processing context
compatibleFormats (Iterable[Optional[str]]) – a list of lowercase file extensions compatible with the algorithm
preferredFormat (Optional[str] = '') – preferred format extension to use if conversion if required
feedback (Optional[QgsProcessingFeedback] = None) -> (str) – feedback object

Returns:

path to source layer, or nearly converted compatible layer
layerName: the target layer name for multi-layer sources (e.g. Geopackage)

Added in version 3.10.

parameterAsConnectionName(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

Evaluates the parameter with matching name to a connection name string.

Added in version 3.14.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsCrs(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsCoordinateReferenceSystem[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

QgsCoordinateReferenceSystem

parameterAsDatabaseTableName(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

Evaluates the parameter with matching name to a database table name string.

Added in version 3.14.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsDateTime(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QDateTime[source]¶

Evaluates the parameter with matching name to a DateTime, or returns an invalid date time if the parameter was not set.

Added in version 3.14.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

QDateTime

parameterAsDouble(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → float[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

float

parameterAsEnum(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → int[source]¶

Evaluates the parameter with matching name to a enum value.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

int

parameterAsEnumString(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

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

Added in version 3.18.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsEnumStrings(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[str][source]¶

Evaluates the parameter with matching name to list of static enum strings.

Added in version 3.18.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[str]

parameterAsEnums(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[int]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[int]

parameterAsExpression(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

Evaluates the parameter with matching name to an expression.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsExtent(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsRectangle[source]¶

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.

See also

parameterAsExtentGeometry()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
crs (QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem())

Return type:

QgsRectangle

parameterAsExtentCrs(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsCoordinateReferenceSystem[source]¶

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

See also

parameterAsExtent()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

QgsCoordinateReferenceSystem

parameterAsExtentGeometry(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsGeometry[source]¶

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).

See also

parameterAsExtent()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
crs (QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem())

Return type:

QgsGeometry

parameterAsFields(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[str][source]¶

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

Deprecated since version 3.40: Use parameterAsStrings() instead.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[str]

parameterAsFile(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsFileList(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[str][source]¶

Evaluates the parameter with matching name to a list of files (for QgsProcessingParameterMultipleLayers in QgsProcessing:TypeFile mode).

Added in version 3.10.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[str]

parameterAsFileOutput(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsGeometry(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsGeometry[source]¶

Evaluates the parameter with matching name to a geometry.

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

See also

parameterAsGeometryCrs()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
crs (QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem())

Return type:

QgsGeometry

parameterAsGeometryCrs(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsCoordinateReferenceSystem[source]¶

Returns the coordinate reference system associated with a geometry parameter value.

See also

parameterAsGeometry()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

QgsCoordinateReferenceSystem

parameterAsInt(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → int[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

int

parameterAsInts(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[int]¶

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

Added in version 3.4.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[int]

parameterAsLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsMapLayer | None[source]¶

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.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsMapLayer]

parameterAsLayerList(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, flags: QgsProcessing.LayerOptionsFlags | QgsProcessing.LayerOptionsFlag = QgsProcessing.LayerOptionsFlags()) → List[QgsMapLayer]¶

Evaluates the parameter with matching name to a list of map layers. The flags are used to set options for loading layers (e.g. skip index generation).

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
flags (Union[QgsProcessing.LayerOptionsFlags, QgsProcessing.LayerOptionsFlag] = QgsProcessing.LayerOptionsFlags())

Return type:

List[QgsMapLayer]

parameterAsLayout(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsPrintLayout | None[source]¶

Evaluates the parameter with matching name to a print layout.

Warning

This method is not safe to run in a background thread, so it must either be used within a prepareAlgorithm implementation (which runs in the main thread), or the algorithm must return the FlagNoThreading flag.

Added in version 3.8.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsPrintLayout]

parameterAsLayoutItem(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, layout: QgsPrintLayout | None) → QgsLayoutItem | None[source]¶

Evaluates the parameter with matching name to a print layout item, taken from the specified layout.

Warning

This method is not safe to run in a background thread, so it must either be used within a prepareAlgorithm implementation (which runs in the main thread), or the algorithm must return the FlagNoThreading flag.

Added in version 3.8.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
layout (Optional[QgsPrintLayout])

Return type:

Optional[QgsLayoutItem]

parameterAsMatrix(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[Any][source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[Any]

parameterAsMeshLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsMeshLayer | None[source]¶

Evaluates the parameter with matching name to a mesh 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.

Added in version 3.6.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsMeshLayer]

parameterAsOutputLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsPoint(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsPointXY[source]¶

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.

See also

parameterAsPointCrs()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
crs (QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem())

Return type:

QgsPointXY

parameterAsPointCloudLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, flags: QgsProcessing.LayerOptionsFlags | QgsProcessing.LayerOptionsFlag = QgsProcessing.LayerOptionsFlags()) → QgsPointCloudLayer | None[source]¶

Evaluates the parameter with matching name to a point cloud layer. The flags are used to set options for loading layer (e.g. skip index generation).

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.

Added in version 3.22.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
flags (Union[QgsProcessing.LayerOptionsFlags, QgsProcessing.LayerOptionsFlag] = QgsProcessing.LayerOptionsFlags())

Return type:

Optional[QgsPointCloudLayer]

parameterAsPointCrs(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsCoordinateReferenceSystem[source]¶

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

See also

parameterAsPoint()

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

QgsCoordinateReferenceSystem

parameterAsRange(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[float]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[float]

parameterAsRasterLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsRasterLayer | None[source]¶

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.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsRasterLayer]

parameterAsSchema(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

Evaluates the parameter with matching name to a database schema name string.

Added in version 3.14.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsSink(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext, fields: QgsFields, geometryType: Qgis.WkbType = Qgis.WkbType.NoGeometry, crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem(), sinkFlags: QgsFeatureSink.SinkFlags | QgsFeatureSink.SinkFlag = QgsFeatureSink.SinkFlags(), createOptions: Dict[str, Any] = {}, datasourceOptions: Iterable[str | None] = [], layerOptions: Iterable[str | None] = [])[source]¶

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().

The createOptions argument is used to pass on creation options such as layer name.

The datasourceOptions and layerOptions arguments is used to pass on GDAL-specific format driver options.

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

Raises:

QgsProcessingException –

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)
fields (QgsFields)
geometryType (Qgis.WkbType = Qgis.WkbType.NoGeometry)
crs (QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem())
sinkFlags (Union[QgsFeatureSink.SinkFlags, QgsFeatureSink.SinkFlag] = QgsFeatureSink.SinkFlags())
createOptions (Dict[str, Any] = {})
datasourceOptions (Iterable[Optional[str]] = [])
layerOptions (Iterable[Optional[str]] = []) -> (Optional[QgsFeatureSink])

parameterAsSource(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsProcessingFeatureSource | None[source]¶

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.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsProcessingFeatureSource]

parameterAsString(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → str[source]¶

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

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

str

parameterAsStrings(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → List[str][source]¶

Evaluates the parameter with matching name to a list of strings (e.g. field names or point cloud attributes).

Added in version 3.32.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

List[str]

parameterAsVectorLayer(self, parameters: Dict[str, Any], name: str | None, context: QgsProcessingContext) → QgsVectorLayer | None[source]¶

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.

Parameters:

parameters (Dict[str, Any])
name (Optional[str])
context (QgsProcessingContext)

Return type:

Optional[QgsVectorLayer]

parameterDefinition(self, name: str | None) → QgsProcessingParameterDefinition | None[source]¶

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

See also

parameterDefinitions()

Parameters:: name (Optional[str])
Return type:: Optional[QgsProcessingParameterDefinition]

parameterDefinitions(self) → List[QgsProcessingParameterDefinition][source]¶

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

See also

addParameter()

See also

parameterDefinition()

See also

destinationParameterDefinitions()

Return type:: List[QgsProcessingParameterDefinition]

postProcess(self, context: QgsProcessingContext, feedback: QgsProcessingFeedback | None, runResult: bool = True) → Dict[str, Any][source]¶

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.

Since QGIS 3.38, postProcess() will always be called even for unsuccessful run executions, to allow the algorithm to gracefully clean up. The runResult argument is used to indicate whether the run was successful. The algorithm’s postProcessAlgorithm() method will only be called when runResult is True.

Parameters:

context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])
runResult (bool = True)

Return type:

Dict[str, Any]

virtual postProcessAlgorithm(self, context: QgsProcessingContext, feedback: QgsProcessingFeedback | None) → Dict[str, Any][source]¶

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.

Return type:: Dict[str, Any]
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().

See also

prepareAlgorithm()

See also

processAlgorithm()

Parameters:

context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])

prepare(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback | None) → bool[source]¶

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])

Return type:

bool

virtual prepareAlgorithm(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback | None) → bool[source]¶

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.

Return type:: bool
Returns:: True if preparation was successful.

See also

processAlgorithm()

See also

postProcessAlgorithm()

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])

virtual preprocessParameters(self, parameters: Dict[str, Any]) → Dict[str, Any][source]¶

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.

Parameters:: parameters (Dict[str, Any])
Return type:: Dict[str, Any]

abstract processAlgorithm(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback | None) → Dict[str, Any][source]¶

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).

Implementations of processAlgorithm can throw the QgsProcessingException exception to indicate that a fatal error occurred within the execution.

Return type:: Dict[str, Any]
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.

See also

prepareAlgorithm()

See also

postProcessAlgorithm()

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])

provider(self) → QgsProcessingProvider | None[source]¶

Returns the provider to which this algorithm belongs.

Return type:: Optional[QgsProcessingProvider]

removeParameter(self, name: str | None)[source]¶

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

Parameters:: name (Optional[str])

run(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback | None, configuration: Dict[str, Any] = {}, catchExceptions: bool = True)[source]¶

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.

If catchExceptions is set to False, then QgsProcessingException raised during the algorithm run will not be automatically caught and will be raised instead.

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])
configuration (Dict[str, Any] = {})
catchExceptions (bool = True) -> (Dict[str, Any])

runPrepared(self, parameters: Dict[str, Any], context: QgsProcessingContext, feedback: QgsProcessingFeedback | None) → Dict[str, Any][source]¶

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)
feedback (Optional[QgsProcessingFeedback])

Return type:

Dict[str, Any]

setProvider(self, provider: QgsProcessingProvider | None)[source]¶

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

Parameters:: provider (Optional[QgsProcessingProvider])

virtual shortDescription(self) → str[source]¶

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.”

Added in version 3.2.

Return type:: str

virtual shortHelpString(self) → str[source]¶

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()

Return type:: str

virtual sinkProperties(self, sink: str | None, parameters: Dict[str, Any], context: QgsProcessingContext, sourceProperties: Dict[str | None, QgsProcessingAlgorithm.VectorProperties]) → QgsProcessingAlgorithm.VectorProperties[source]¶

Returns the vector properties which will be used for the sink with matching name.

The parameters argument specifies the values of all parameters which would be used to generate the sink. These can be used alongside the provided context in order to pre-evaluate inputs when required in order to determine the sink’s properties.

The sourceProperties map will contain the vector properties of the various sources used as inputs to the algorithm. These will only be available in certain circumstances (e.g. when the algorithm is used within a model), so implementations will need to be adaptable to circumstances when either sourceParameters is empty or parameters is empty, and use whatever information is passed in order to make a best guess determination of the output properties.

Added in version 3.14.

Parameters:

sink (Optional[str])
parameters (Dict[str, Any])
context (QgsProcessingContext)
sourceProperties (Dict[Optional[str], QgsProcessingAlgorithm.VectorProperties])

Return type:

QgsProcessingAlgorithm.VectorProperties

virtual supportInPlaceEdit(self, layer: QgsMapLayer | None) → bool[source]¶

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

Return type:: bool
Returns:: True if the algorithm supports in-place editing

Added in version 3.4.

Parameters:: layer (Optional[QgsMapLayer])

virtual svgIconPath(self) → str[source]¶

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

See also

icon()

Return type:: str

virtual tags(self) → List[str][source]¶

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.

Return type:: List[str]

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

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.

Parameters:

parameters (Dict[str, Any])
context (QgsProcessingContext)

Return type:

bool

static writeFeatureError(sink: QgsFeatureSink | None, parameters: Dict[str, Any], name: str | None) → str[source]¶

Returns a user-friendly string to use as an error when a feature cannot be written into a sink.

The sink argument is the sink into which the feature cannot be written.

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

Added in version 3.22.

Parameters:

sink (Optional[QgsFeatureSink])
parameters (Dict[str, Any])
name (Optional[str])

Return type:

str