Class: QgsProperty¶

class qgis.core.QgsProperty¶

Bases: sip.wrapper

Constructor for a QgsAbstractProperty. The property will be set to an InvalidProperty type.

QgsProperty(other: QgsProperty) Copy constructor

A store for object properties.

QgsProperty objects are used for storing properties for objects, which can then be transformed to a QVariant value by evaluating them against a supplied QgsExpressionContext. Multiple QgsProperty objects can be grouped using a QgsPropertyCollection for easier bulk storage, retrieval and evaluation.

QgsProperty objects are implicitly shared and can be inexpensively copied.

New in version 3.0: Enums

Methods

`asExpression`	Returns an expression string representing the state of the property, or an empty string if the property could not be converted to an expression
`convertToTransformer`	Attempts to convert an existing expression based property to a base expression with corresponding transformer.
`expressionString`	Returns the expression used for the property value.
`field`	Returns the current field name the property references.
`fromExpression`	Returns a new ExpressionBasedProperty created from the specified expression.
`fromField`	Returns a new FieldBasedProperty created from the specified field name.
`fromValue`	Returns a new StaticProperty created from the specified value.
`isActive`	Returns whether the property is currently active.
`isProjectColor`	Returns `True` if the property is set to a linked project color.
`loadVariant`	Loads this property from a QVariantMap, wrapped in a QVariant.
`prepare`	Prepares the property against a specified expression context.
`propertyType`	Returns the property type.
`referencedFields`	Returns the set of any fields referenced by the property for a specified expression context.
`setActive`	Sets whether the property is currently active.
`setExpressionString`	Sets the expression to use for the property value.
`setField`	Sets the field name the property references.
`setStaticValue`	Sets the static value for the property.
`setTransformer`	Sets an optional transformer to use for manipulating the calculated values for the property.
`staticValue`	Returns the current static value for the property.
`toVariant`	Saves this property to a QVariantMap, wrapped in a QVariant.
`transformer`	Returns the existing transformer used for manipulating the calculated values for the property, if set.
`value`	Calculates the current value of the property, including any transforms which are set for the property
`valueAsBool`	Calculates the current value of the property and interprets it as an boolean.
`valueAsColor`	Calculates the current value of the property and interprets it as a color.
`valueAsDouble`	Calculates the current value of the property and interprets it as a double.
`valueAsInt`	Calculates the current value of the property and interprets it as an integer.
`valueAsString`	Calculates the current value of the property and interprets it as a string.

Signals

Attributes

`ExpressionBasedProperty`
`FieldBasedProperty`
`InvalidProperty`
`StaticProperty`

ExpressionBasedProperty = 3¶

FieldBasedProperty = 2¶

InvalidProperty = 0¶

StaticProperty = 1¶

class Type¶: Bases: int

asExpression(self) → str¶: Returns an expression string representing the state of the property, or an empty string if the property could not be converted to an expression

convertToTransformer(self) → bool¶: Attempts to convert an existing expression based property to a base expression with corresponding transformer. Returns True if conversion was successful. Note that calling this method requires multiple parsing of expressions, so it should only be called in non-performance critical code.

expressionString(self) → str¶: Returns the expression used for the property value. If the property is not a ExpressionBasedProperty this will return an empty string.

See also

setExpressionString()

field(self) → str¶: Returns the current field name the property references. If the property is not a FieldBasedProperty this will return an empty string.

See also

setField()

fromExpression(expression: str, isActive: bool = True) → QgsProperty¶: Returns a new ExpressionBasedProperty created from the specified expression.

fromField(fieldName: str, isActive: bool = True) → QgsProperty¶: Returns a new FieldBasedProperty created from the specified field name.

fromValue(value: Any, isActive: bool = True) → QgsProperty¶: Returns a new StaticProperty created from the specified value.

isActive(self) → bool¶: Returns whether the property is currently active.

See also

setActive()

isProjectColor(self) → bool¶: Returns True if the property is set to a linked project color.

New in version 3.6.

loadVariant(self, property: Any) → bool¶: Loads this property from a QVariantMap, wrapped in a QVariant. You can use QgsXmlUtils.readVariant to load it from an XML document.

See also

toVariant()

prepare(self, context: QgsExpressionContext = QgsExpressionContext()) → bool¶: Prepares the property against a specified expression context. Calling prepare before evaluating the property multiple times allows precalculation of expensive setup tasks such as parsing expressions. Returns True if preparation was successful.

propertyType(self) → QgsProperty.Type¶: Returns the property type.

referencedFields(self, context: QgsExpressionContext = QgsExpressionContext()) → Set[str]¶: Returns the set of any fields referenced by the property for a specified expression context.

setActive(self, active: bool)¶: Sets whether the property is currently active.

See also

isActive()

setExpressionString(self, expression: str)¶: Sets the expression to use for the property value. Calling this will transform the property into an ExpressionBasedProperty.

See also

expressionString()

setField(self, field: str)¶: Sets the field name the property references. Calling this will transform the property into an FieldBasedProperty.

See also

field()

setStaticValue(self, value: Any)¶: Sets the static value for the property. Calling this will transform the property into an StaticProperty.

See also

staticValue()

setTransformer(self, transformer: QgsPropertyTransformer)¶

Sets an optional transformer to use for manipulating the calculated values for the property.

Parameters: transformer – transformer to install. Ownership is transferred to the property, and any existing transformer will be deleted. Set to None to remove an existing transformer.

See also

transformer()

staticValue(self) → Any¶: Returns the current static value for the property. If the property is not a StaticProperty this will return an invalid variant.

See also

setStaticValue()

toVariant(self) → Any¶: Saves this property to a QVariantMap, wrapped in a QVariant. You can use QgsXmlUtils.writeVariant to save it to an XML document.

See also

loadVariant()

transformer(self) → QgsPropertyTransformer¶: Returns the existing transformer used for manipulating the calculated values for the property, if set.

See also

setTransformer()

value(self, context: QgsExpressionContext, defaultValue: Any = None) → Tuple[Any, bool]¶

Calculates the current value of the property, including any transforms which are set for the property

Parameters

context – QgsExpressionContext to evaluate the property for. The variables and functions contained in the expression context can be used to alter the calculated value for the property, so that a property is able to respond to the current environment, layers and features within QGIS.
defaultValue – default value to return if the property is not active or cannot be calculated

Returns

calculated value for property
ok: will be set to True if conversion was successful

See also

See also

See also

See also

See also

valueAsBool(self, context: QgsExpressionContext, defaultValue: bool = False) → Tuple[bool, bool]¶

Calculates the current value of the property and interprets it as an boolean.

Parameters

context – QgsExpressionContext to evaluate the property for.
defaultValue – default boolean to return if the property cannot be calculated as an boolean

Returns

value parsed to boolean
ok: will be set to True if conversion was successful

See also

See also

See also

See also

See also

valueAsColor(self, context: QgsExpressionContext, defaultColor: Union[QColor, Qt.GlobalColor, QGradient] = QColor()) → Tuple[QColor, bool]¶

Calculates the current value of the property and interprets it as a color.

Parameters

context – QgsExpressionContext to evaluate the property for.
defaultColor – default color to return if the property cannot be calculated as a color

Returns

value parsed to color
ok: will be set to True if conversion was successful

See also

See also

See also

See also

See also

valueAsDouble(self, context: QgsExpressionContext, defaultValue: float = 0) → Tuple[float, bool]¶

Calculates the current value of the property and interprets it as a double.

Parameters

context – QgsExpressionContext to evaluate the property for.
defaultValue – default double to return if the property cannot be calculated as a double

Returns

value parsed to double
ok: will be set to True if conversion was successful

See also

See also

See also

See also

See also

valueAsInt(self, context: QgsExpressionContext, defaultValue: int = 0) → Tuple[int, bool]¶

Calculates the current value of the property and interprets it as an integer.

Parameters

context – QgsExpressionContext to evaluate the property for.
defaultValue – default integer to return if the property cannot be calculated as an integer

Returns

value parsed to integer
ok: will be set to True if conversion was successful

See also

See also

See also

See also

See also

valueAsString(self, context: QgsExpressionContext, defaultString: str = '') → Tuple[str, bool]¶

Calculates the current value of the property and interprets it as a string.

Parameters

context – QgsExpressionContext to evaluate the property for.
defaultString – default string to return if the property cannot be calculated as a string

Returns