Class: QgsExpressionContextUtils¶

Contains utilities for working with QgsExpressionContext objects, including methods for creating scopes for specific uses (e.g., project scopes, layer scopes).

Static Methods

`atlasScope`	Creates a new scope which contains variables and functions relating to a `QgsLayoutAtlas`.
`createFeatureBasedContext`	Helper function for creating an expression context which contains just a feature and fields collection.
`formScope`	Creates a new scope which contains functions and variables from the current attribute form/table formFeature.
`globalProjectLayerScopes`	Creates a list of three scopes: global, layer's project and layer.
`globalScope`	Creates a new scope which contains variables and functions relating to the global QGIS context.
`layerScope`	Creates a new scope which contains variables and functions relating to a `QgsMapLayer`.
`layoutItemScope`	Creates a new scope which contains variables and functions relating to a `QgsLayoutItem`.
`layoutScope`	Creates a new scope which contains variables and functions relating to a `QgsLayout` layout.
`mapLayerPositionScope`	Sets the expression context variables which are available for expressions triggered by moving the mouse over a feature of the currently selected layer.
`mapSettingsScope`	Creates a new scope which contains variables and functions relating to a `QgsMapSettings` object.
`mapToolCaptureScope`	Sets the expression context variables which are available for expressions triggered by a map tool capture like add feature.
`meshExpressionScope`	Creates a new scope which contains functions relating to mesh layer element elementType
`multiFrameScope`	Creates a new scope which contains variables and functions relating to a `QgsLayoutMultiFrame`.
`notificationScope`	Creates a new scope which contains variables and functions relating to provider notifications
`parentFormScope`	Creates a new scope which contains functions and variables from the current parent attribute form/table formFeature.
`processingAlgorithmScope`	Creates a new scope which contains variables and functions relating to a processing algorithm, when used with the specified parameters and context.
`processingModelAlgorithmScope`	Creates a new scope which contains variables and functions relating to a processing model algorithm, when used with the specified parameters and context.
`projectScope`	Creates a new scope which contains variables and functions relating to a QGIS project.
`registerContextFunctions`	Registers all known core functions provided by `QgsExpressionContextScope` objects.
`removeGlobalVariable`	Remove a global context variable.
`removeProjectVariable`	Remove project context variable.
`setGlobalVariable`	Sets a global context variable.
`setGlobalVariables`	Sets all global context variables.
`setLayerVariable`	Sets a layer context variable.
`setLayerVariables`	Sets all layer context variables.
`setLayoutItemVariable`	Sets a layout item context variable, with the given name and value.
`setLayoutItemVariables`	Sets all layout item context variables for an item.
`setLayoutMultiFrameVariable`	Sets a layout multi frame context variable, with the given name and value.
`setLayoutMultiFrameVariables`	Sets all layout multiframe context variables for an frame.
`setLayoutVariable`	Sets a layout context variable.
`setLayoutVariables`	Sets all layout context variables.
`setProjectVariable`	Sets a project context variable.
`setProjectVariables`	Sets all project context variables.
`updateSymbolScope`	Updates a symbol scope related to a `QgsSymbol` to an expression context.

class qgis.core.QgsExpressionContextUtils[source]¶

Bases: object

static atlasScope(atlas: QgsLayoutAtlas | None) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QgsLayoutAtlas. For instance, current page name and number.

Parameters:: atlas (Optional[QgsLayoutAtlas]) – source atlas. If None, a set of default atlas variables will be added to the scope.
Return type:: Optional[QgsExpressionContextScope]

static createFeatureBasedContext(feature: QgsFeature, fields: QgsFields) → QgsExpressionContext[source]¶

Helper function for creating an expression context which contains just a feature and fields collection. Generally this method should not be used as the created context does not include standard scopes such as the global and project scopes.

Parameters:

feature (QgsFeature)
fields (QgsFields)

Return type:

QgsExpressionContext

static formScope(formFeature: QgsFeature = QgsFeature(), formMode: str | None = '') → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains functions and variables from the current attribute form/table formFeature. The variables and values in this scope will reflect the current state of the form/row being edited. The formMode (SingleEditMode etc.) is passed as text

Added in version 3.2.

Parameters:

formFeature (QgsFeature = QgsFeature())
formMode (Optional[str] = '')

Return type:

Optional[QgsExpressionContextScope]

static globalProjectLayerScopes(layer: QgsMapLayer | None) → List[QgsExpressionContextScope]¶

Creates a list of three scopes: global, layer’s project and layer.

Parameters:: layer (Optional[QgsMapLayer])
Return type:: List[QgsExpressionContextScope]

static globalScope() → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to the global QGIS context. For instance, QGIS version numbers and variables specified through QGIS options.

See also

setGlobalVariable()

Return type:: Optional[QgsExpressionContextScope]

static layerScope(layer: QgsMapLayer | None) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QgsMapLayer. For instance, layer name, id and fields.

Parameters:: layer (Optional[QgsMapLayer])
Return type:: Optional[QgsExpressionContextScope]

static layoutItemScope(item: QgsLayoutItem | None) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QgsLayoutItem. For instance, item size and position.

See also

setLayoutItemVariable()

See also

setLayoutItemVariables()

Parameters:: item (Optional[QgsLayoutItem])
Return type:: Optional[QgsExpressionContextScope]

static layoutScope(layout: QgsLayout | None) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QgsLayout layout. For instance, number of pages and page sizes.

Parameters:: layout (Optional[QgsLayout])
Return type:: Optional[QgsExpressionContextScope]

static mapLayerPositionScope(position: QgsPointXY) → QgsExpressionContextScope | None[source]¶

Sets the expression context variables which are available for expressions triggered by moving the mouse over a feature of the currently selected layer.

Parameters:: position (QgsPointXY) – map coordinates of the current pointer position in the CRS of the layer which triggered the action.

Added in version 3.30.

Return type:: Optional[QgsExpressionContextScope]

static mapSettingsScope(mapSettings: QgsMapSettings) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QgsMapSettings object. For instance, map scale and rotation.

Parameters:: mapSettings (QgsMapSettings)
Return type:: Optional[QgsExpressionContextScope]

static mapToolCaptureScope(matches: Iterable[QgsPointLocator.Match]) → QgsExpressionContextScope | None[source]¶

Sets the expression context variables which are available for expressions triggered by a map tool capture like add feature.

Parameters:: matches (Iterable[QgsPointLocator.Match])
Return type:: Optional[QgsExpressionContextScope]

static meshExpressionScope(elementType: QgsMesh.ElementType) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains functions relating to mesh layer element elementType

Added in version 3.22.

Parameters:: elementType (QgsMesh.ElementType)
Return type:: Optional[QgsExpressionContextScope]

static multiFrameScope(frame: QgsLayoutMultiFrame | None) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QgsLayoutMultiFrame.

See also

setLayoutMultiFrameVariable()

See also

setLayoutMultiFrameVariables()

Added in version 3.10.

Parameters:: frame (Optional[QgsLayoutMultiFrame])
Return type:: Optional[QgsExpressionContextScope]

static notificationScope(message: str | None = '') → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to provider notifications

Parameters:: message (Optional[str] = '') – the notification message
Return type:: Optional[QgsExpressionContextScope]

static parentFormScope(formFeature: QgsFeature = QgsFeature(), formMode: str | None = '') → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains functions and variables from the current parent attribute form/table formFeature. The variables and values in this scope will reflect the current state of the parent form/row being edited. The formMode (SingleEditMode etc.) is passed as text

Added in version 3.14.

Parameters:

formFeature (QgsFeature = QgsFeature())
formMode (Optional[str] = '')

Return type:

Optional[QgsExpressionContextScope]

static processingAlgorithmScope(algorithm: QgsProcessingAlgorithm | None, parameters: Dict[str, Any], context: QgsProcessingContext) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a processing algorithm, when used with the specified parameters and context. For instance, algorithm name and parameter functions.

See also

processingModelAlgorithmScope()

Parameters:

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

Return type:

Optional[QgsExpressionContextScope]

static processingModelAlgorithmScope(model: QgsProcessingModelAlgorithm | None, parameters: Dict[str, Any], context: QgsProcessingContext) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a processing model algorithm, when used with the specified parameters and context. For instance, model name and path variables.

Added in version 3.6.

Parameters:

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

Return type:

Optional[QgsExpressionContextScope]

static projectScope(project: QgsProject | None) → QgsExpressionContextScope | None[source]¶

Creates a new scope which contains variables and functions relating to a QGIS project. For instance, project path and title, and variables specified through the project properties.

Parameters:: project (Optional[QgsProject]) – What project to use

See also

setProjectVariable()

Return type:: Optional[QgsExpressionContextScope]

static registerContextFunctions()[source]¶: Registers all known core functions provided by QgsExpressionContextScope objects.

static removeGlobalVariable(name: str | None)[source]¶

Remove a global context variable.

Parameters:: name (Optional[str]) – variable name

See also

setGlobalVariable()

See also

setGlobalVariables()

See also

globalScope()

static removeProjectVariable(project: QgsProject | None, name: str | None)[source]¶

Remove project context variable.

Parameters:

project (Optional[QgsProject]) – Project to apply changes to
name (Optional[str]) – variable name

See also

setProjectVariable()

See also

setProjectVariables()

See also

projectScope()

static setGlobalVariable(name: str | None, value: Any)[source]¶

Sets a global context variable. This variable will be contained within scopes retrieved via globalScope().

Parameters:

name (Optional[str]) – variable name
value (Any) – variable value

See also

setGlobalVariable()

See also

globalScope()

See also

removeGlobalVariable()

static setGlobalVariables(variables: Dict[str, Any])[source]¶

Sets all global context variables. Existing global variables will be removed and replaced with the variables specified.

Parameters:: variables (Dict[str, Any]) – new set of global variables

See also

setGlobalVariable()

See also

globalScope()

See also

removeGlobalVariable()

static setLayerVariable(layer: QgsMapLayer | None, name: str | None, value: Any)[source]¶

Sets a layer context variable. This variable will be contained within scopes retrieved via layerScope().

Parameters:

layer (Optional[QgsMapLayer]) – map layer
name (Optional[str]) – variable name
value (Any) – variable value

See also

setLayerVariables()

See also

layerScope()

static setLayerVariables(layer: QgsMapLayer | None, variables: Dict[str, Any])[source]¶

Sets all layer context variables. Existing layer variables will be removed and replaced with the variables specified.

Parameters:

layer (Optional[QgsMapLayer]) – map layer
variables (Dict[str, Any]) – new set of layer variables

See also

setLayerVariable()

See also

layerScope()

static setLayoutItemVariable(item: QgsLayoutItem | None, name: str | None, value: Any)[source]¶

Sets a layout item context variable, with the given name and value. This variable will be contained within scopes retrieved via layoutItemScope().

See also

setLayoutItemVariables()

See also

layoutItemScope()

Parameters:

item (Optional[QgsLayoutItem])
name (Optional[str])
value (Any)

static setLayoutItemVariables(item: QgsLayoutItem | None, variables: Dict[str, Any])[source]¶

Sets all layout item context variables for an item. Existing variables will be removed and replaced with the variables specified.

See also

setLayoutItemVariable()

See also

layoutItemScope()

Parameters:

item (Optional[QgsLayoutItem])
variables (Dict[str, Any])

static setLayoutMultiFrameVariable(frame: QgsLayoutMultiFrame | None, name: str | None, value: Any)[source]¶

Sets a layout multi frame context variable, with the given name and value. This variable will be contained within scopes retrieved via multiFrameScope().

See also

setLayoutItemVariables()

See also

multiFrameScope()

Added in version 3.10.

Parameters:

frame (Optional[QgsLayoutMultiFrame])
name (Optional[str])
value (Any)

static setLayoutMultiFrameVariables(frame: QgsLayoutMultiFrame | None, variables: Dict[str, Any])[source]¶

Sets all layout multiframe context variables for an frame. Existing variables will be removed and replaced with the variables specified.

See also

setLayoutMultiFrameVariable()

See also

multiFrameScope()

Added in version 3.10.

Parameters:

frame (Optional[QgsLayoutMultiFrame])
variables (Dict[str, Any])

static setLayoutVariable(layout: QgsLayout | None, name: str | None, value: Any)[source]¶

Sets a layout context variable. This variable will be contained within scopes retrieved via layoutScope().

Parameters:

layout (Optional[QgsLayout]) – target layout
name (Optional[str]) – variable name
value (Any) – variable value

See also

setLayoutVariables()

See also

layoutScope()

static setLayoutVariables(layout: QgsLayout | None, variables: Dict[str, Any])[source]¶

Sets all layout context variables. Existing layout variables will be removed and replaced with the variables specified.

Parameters:

layout (Optional[QgsLayout]) – target layout
variables (Dict[str, Any]) – new set of layer variables

See also

setLayoutVariable()

See also

layoutScope()

static setProjectVariable(project: QgsProject | None, name: str | None, value: Any)[source]¶

Sets a project context variable. This variable will be contained within scopes retrieved via projectScope().

Parameters:

project (Optional[QgsProject]) – Project to apply changes to
name (Optional[str]) – variable name
value (Any) – variable value

See also

setProjectVariables()

See also

removeProjectVariable()

See also

projectScope()

static setProjectVariables(project: QgsProject | None, variables: Dict[str, Any])[source]¶

Sets all project context variables. Existing project variables will be removed and replaced with the variables specified.

Parameters:

project (Optional[QgsProject]) – Project to apply changes to
variables (Dict[str, Any]) – new set of project variables

See also

setProjectVariable()

See also

removeProjectVariable()

See also

projectScope()

static updateSymbolScope(symbol: QgsSymbol | None, symbolScope: QgsExpressionContextScope | None = None) → QgsExpressionContextScope | None[source]¶

Updates a symbol scope related to a QgsSymbol to an expression context.

Parameters:

symbol (Optional[QgsSymbol]) – symbol to extract properties from
symbolScope (Optional[QgsExpressionContextScope] = None) – pointer to an existing scope to update

Return type:

Optional[QgsExpressionContextScope]