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: Enums
Methods
Adds an output
definition
to the algorithm.Adds a parameter
definition
to the algorithm.Returns a Python command string which can be executed to run the algorithm using the specified
parameters
.Returns true if the algorithm can execute.
Checks the supplied
parameter
values to verify that they satisfy the requirements of this algorithm in the suppliedcontext
.Returns the number of visible (non-hidden) parameters defined by this algorithm.
Creates a copy of the algorithm, ready for execution.
If an algorithm subclass implements a custom parameters widget, a copy of this widget should be constructed and returned by this method.
Creates an expression context relating to the algorithm.
Creates a new instance of the algorithm class.
Returns a list of destination parameters definitions utilized by the algorithm.
Returns the translated algorithm name, which should be used for any user-visible display of the algorithm name.
Returns the flags indicating how and when the algorithm operates and should be exposed to users.
Returns the name of the group this algorithm belongs to.
Returns the unique ID of the group this algorithm belongs to.
Returns true if this algorithm generates HTML outputs.
Returns a localised help string for the algorithm.
Returns a url pointing to the algorithm’s help page.
Returns an icon for the algorithm.
Returns the unique ID for the algorithm, which is a combination of the algorithm provider’s ID and the algorithms unique name (e.g.
Initializes the algorithm using the specified
configuration
.Returns a user-friendly string to use as an error when a raster layer input could not be loaded.
Returns a user-friendly string to use as an error when a sink parameter could not be created.
Returns a user-friendly string to use as an error when a source parameter could not be loaded.
Returns the algorithm name, used for identifying the algorithm.
Returns a matching output by
name
.Returns an ordered list of output definitions utilized by the algorithm.
Evaluates the parameter with matching
name
to a static boolean value.Evaluates the parameter with matching
name
to a source vector layer file path of compatible format.Evaluates the parameter with matching
name
to a coordinate reference system.Evaluates the parameter with matching
name
to a static double value.Evaluates the parameter with matching
name
to a enum value.Evaluates the parameter with matching
name
to list of enum values.Evaluates the parameter with matching
name
to an expression.Evaluates the parameter with matching
name
to a rectangular extent.Returns the coordinate reference system associated with an extent parameter value.
Evaluates the parameter with matching
name
to a rectangular extent, and returns a geometry covering this extent.Evaluates the parameter with matching
name
to a list of fields.Evaluates the parameter with matching
name
to a file/folder name.Evaluates the parameter with matching
name
to a file based output destination.Evaluates the parameter with matching
name
to a static integer value.Evaluates the parameter with matching
name
to a list of integer values.Evaluates the parameter with matching
name
to a map layer.Evaluates the parameter with matching
name
to a list of map layers.Evaluates the parameter with matching
name
to a matrix/table of values.Evaluates the parameter with matching
name
to a mesh layer.Evaluates the parameter with matching
name
to a output layer destination.Evaluates the parameter with matching
name
to a point.Returns the coordinate reference system associated with an point parameter value.
Evaluates the parameter with matching
name
to a range of values.Evaluates the parameter with matching
name
to a raster layer.Evaluates the parameter with matching
name
to a feature sink.Evaluates the parameter with matching
name
to a feature source.Evaluates the parameter with matching
name
to a static string value.Evaluates the parameter with matching
name
to a vector layer.Returns a matching parameter by
name
.Returns an ordered list of parameter definitions utilized by the algorithm.
Should be called in the main thread following the completion of runPrepared().
Allows the algorithm to perform any required cleanup tasks.
Prepares the algorithm for execution.
Prepares the algorithm to run using the specified
parameters
.Pre-processes a set of
parameters
, allowing the algorithm to clean their values.Runs the algorithm using the specified
parameters
.Returns the provider to which this algorithm belongs.
Removes the parameter with matching
name
from the algorithm, and deletes any existing definition.Executes the algorithm using the specified
parameters
.Runs the algorithm, which has been prepared by an earlier call to prepare().
Associates this algorithm with its provider.
Returns an optional translated short description of the algorithm.
Returns a localised short helper string for the algorithm.
Checks whether this algorithm supports in-place editing on the given
layer
Default implementation returns false.Returns a path to an SVG version of the algorithm’s icon.
Returns a list of tags which relate to the algorithm, and are used to assist users in searching for suitable algorithms.
Checks whether the coordinate reference systems for the specified set of
parameters
are valid for the algorithm.Signals
Attributes
-
class
Flag
¶ Bases:
int
-
FlagCanCancel
= 16¶
-
FlagDeprecated
= 6¶
-
FlagDisplayNameIsLiteral
= 128¶
-
FlagHideFromModeler
= 4¶
-
FlagHideFromToolbox
= 2¶
-
FlagKnownIssues
= 512¶
-
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
See also
-
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 aQgsProcessingParameterVectorDestination
andcreateOutput
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. IfcreateOutput
is false then this automatic output creation will not occur.See also
See also
-
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 suppliedcontext
. Themessage
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.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
-
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.
See also
-
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
See also
-
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
See also
-
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
-
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
See also
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
See also
-
icon
(self) → QIcon¶ Returns an icon for the algorithm.
See also
-
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
See also
-
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
See also
-
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 thename
should correspond to the invalid source parameter name.See also
See also
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 thename
should correspond to the invalid source parameter name.See also
See also
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 thename
should correspond to the invalid source parameter name.See also
See also
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
See also
See also
-
outputDefinition
(self, name: str) → QgsProcessingOutputDefinition¶ Returns a matching output by
name
. Matching is done in a case-insensitive manner.See also
-
outputDefinitions
(self) → object¶ Returns an ordered list of output definitions utilized by the algorithm.
See also
See also
-
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 specifiedcrs
. In this case the extent of the reproject rectangle will be returned.See also
-
parameterAsExtentCrs
(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsCoordinateReferenceSystem¶ Returns the coordinate reference system associated with an extent parameter value.
See also
-
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 specifiedcrs
. 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
-
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 thecontext
. 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.
-
parameterAsMeshLayer
(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsMeshLayer¶ 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 thecontext
. In either case, callers do not need to handle deletion of the returned layer.New in version 3.6.
-
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 specifiedcrs
.See also
-
parameterAsPointCrs
(self, parameters: Dict[str, Any], name: str, context: QgsProcessingContext) → QgsCoordinateReferenceSystem¶ Returns the coordinate reference system associated with an point parameter value.
See also
-
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 thecontext
. 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 thecontext
.The
fields
,geometryType
andcrs
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 callingQgsProcessingUtils.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 thecontext
.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 thecontext
. 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.See also
-
parameterDefinitions
(self) → object¶ Returns an ordered list of parameter definitions utilized by the algorithm.
See also
See also
See also
-
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 checkfeedback
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().
See also
See also
-
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
See also
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 checkfeedback
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.
See also
See also
-
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 checkfeedback
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.
See also
See also
-
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 andQgsProcessingProvider
.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
See also
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.
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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
See also
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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.
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.
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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 ifparameters
have passed the CRS check.
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class