Subgroup: Processing

Class: QgsProcessingUtils

class qgis.core.QgsProcessingUtils

Bases: sip.wrapper

Utility functions for use with processing classes.

New in version 3.0: Methods

combineFields Combines two field lists, avoiding duplicate field names (in a case-insensitive manner).
combineLayerExtents Combines the extent of several map layers.
compatibleLayers Returns a list of map layers from a project which are compatible with the processing framework.
compatibleRasterLayers Returns a list of raster layers from a project which are compatible with the processing framework.
compatibleVectorLayers Returns a list of vector layers from a project which are compatible with the processing framework.
convertToCompatibleFormat Converts a source vector layer to a file path to a vector layer of compatible format.
createFeatureSink Creates a feature sink ready for adding features.
fieldNamesToIndices Returns a list of field indices parsed from the given list of field names.
formatHelpMapAsHtml Returns a HTML formatted version of the help text encoded in a variant map for a specified algorithm.
generateIteratingDestination Converts an input parameter value for use in source iterating mode, where one individual sink is created per input feature.
generateTempFilename Returns a temporary filename for a given file, putting it into a temporary folder (creating that folder in the process), but not changing the basename.
indicesToFields Returns a subset of fields based on the indices of desired fields.
mapLayerFromString Interprets a string as a map layer within the supplied context.
normalizeLayerSource Normalizes a layer source string for safe comparison across different operating system environments.
stringToPythonLiteral Converts a string to a Python string literal.
tempFolder Returns a session specific processing temporary folder for use in processing algorithms.
variantToSource Converts a variant value to a new feature source.

Signals

Attributes

Raster
UnknownType
Vector
class LayerHint

Bases: int

Raster = 2
UnknownType = 0
Vector = 1
combineFields(fieldsA: QgsFields, fieldsB: QgsFields) → QgsFields

Combines two field lists, avoiding duplicate field names (in a case-insensitive manner).

Duplicate field names will be altered to “name_2”, “name_3”, etc, finding the first non-duplicate name.

Note

Some output file formats (e.g. shapefiles) have restrictions on the maximum length of field names, so be aware that the results of calling this method may be truncated when saving to these formats.

combineLayerExtents(layers: Iterable[QgsMapLayer], crs: QgsCoordinateReferenceSystem = QgsCoordinateReferenceSystem()) → QgsRectangle

Combines the extent of several map layers. If specified, the target crs will be used to transform the layer’s extent to the desired output reference system.

compatibleLayers(project: QgsProject, sort: bool = True) → List[QgsMapLayer]

Returns a list of map layers from a project which are compatible with the processing framework.

If the sort argument is true then the layers will be sorted by their QgsMapLayer.name() value.

compatibleRasterLayers(project: QgsProject, sort: bool = True) → object

Returns a list of raster layers from a project which are compatible with the processing framework.

If the sort argument is true then the layers will be sorted by their QgsMapLayer.name() value.

compatibleVectorLayers(project: QgsProject, sourceTypes: Iterable[int] = [], sort: bool = True) → List[QgsVectorLayer]

Returns a list of vector layers from a project which are compatible with the processing framework.

The sourceTypes list should be filled with a list of QgsProcessing.SourceType values. If the sourceTypes list is non-empty then the layers will be sorted so that only layers with the specified source type included in the list will be returned. Leaving the sourceTypes list empty will cause all vector layers, regardless of their geometry type, to be returned.

If the sort argument is true then the layers will be sorted by their QgsMapLayer.name() value.

convertToCompatibleFormat(layer: QgsVectorLayer, selectedFeaturesOnly: bool, baseName: str, compatibleFormats: Iterable[str], preferredFormat: str, context: QgsProcessingContext, feedback: QgsProcessingFeedback) → str

Converts a source vector layer to a file path to a vector layer of compatible format.

If the specified 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 using baseName. 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.

createFeatureSink(destination: str, context: QgsProcessingContext, fields: QgsFields, geometryType: QgsWkbTypes.Type, crs: QgsCoordinateReferenceSystem, createOptions: Dict[str, Any] = {}) → Tuple[QgsFeatureSink, str]

Creates a feature sink ready for adding features. The destination specifies a destination URI for the resultant layer. It may be updated in place to reflect the actual destination for the layer.

Sink parameters such as desired fields, geometryType and crs must be specified.

The createOptions map can be used to specify additional sink creation options, which are passed to the underlying provider when creating new layers. Known options also include ‘fileEncoding’, which is used to specify a file encoding to use for created files. If ‘fileEncoding’ is not specified, the default encoding from the context will be used.

If a layer is created for the feature sink, the layer will automatically be added to the context’s temporary layer store.

Note

this version of the createFeatureSink() function has an API designed around use from the SIP bindings. c++ code should call the other createFeatureSink() version.

Note

available in Python bindings as createFeatureSink()

fieldNamesToIndices(fieldNames: Iterable[str], fields: QgsFields) → List[int]

Returns a list of field indices parsed from the given list of field names. Unknown field names are ignored. If the list of field names is empty, it is assumed that all fields are required.

New in version 3.2.

formatHelpMapAsHtml(map: Dict[str, Any], algorithm: QgsProcessingAlgorithm) → str

Returns a HTML formatted version of the help text encoded in a variant map for a specified algorithm.

generateIteratingDestination(input: Any, id: Any, context: QgsProcessingContext) → Any

Converts an input parameter value for use in source iterating mode, where one individual sink is created per input feature. The id parameter represents the unique ID for this output, which is embedded into the resulting parameter value.

generateTempFilename(basename: str) → str

Returns a temporary filename for a given file, putting it into a temporary folder (creating that folder in the process), but not changing the basename.

See also

tempFolder()

indicesToFields(indices: Iterable[int], fields: QgsFields) → QgsFields

Returns a subset of fields based on the indices of desired fields.

New in version 3.2.

mapLayerFromString(string: str, context: QgsProcessingContext, allowLoadingNewLayers: bool = True, typeHint: QgsProcessingUtils.LayerHint = QgsProcessingUtils.UnknownType) → QgsMapLayer

Interprets a string as a map layer within the supplied context.

The method will attempt to load a layer matching the passed string. E.g. if the string matches a layer ID or name within the context’s project or temporary layer store then this layer will be returned. If the string is a file path and allowLoadingNewLayers is true, then the layer at this file path will be loaded and added to the context’s temporary layer store. Ownership of the layer remains with the context or the context’s current project.

The typeHint can be used to dictate the type of map layer expected.

normalizeLayerSource(source: str) → str

Normalizes a layer source string for safe comparison across different operating system environments.

stringToPythonLiteral(string: str) → str

Converts a string to a Python string literal. E.g. by replacing ‘ with ‘.

tempFolder() → str

Returns a session specific processing temporary folder for use in processing algorithms.

variantToSource(value: Any, context: QgsProcessingContext, fallbackValue: Any = None) → QgsProcessingFeatureSource

Converts a variant value to a new feature source.

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

The optional fallbackValue can be used to specify a “default” value which is used if value cannot be successfully converted to a source.

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