Class: QgsExpressionNode

class qgis.core.QgsExpressionNode

Bases: sip.wrapper

Abstract base class for all nodes that can appear in an expression.

Methods

clone

Generate a clone of this node.

dump

Dump this node into a serialized (part) of an expression.

eval

Evaluate this node with the given context and parent.

isStatic

Returns True if this node can be evaluated for a static value.

needsGeometry

Abstract virtual method which returns if the geometry is required to evaluate this expression.

nodeType

Gets the type of this node.

prepare

Prepare this node for evaluation.

referencedColumns

Abstract virtual method which returns a list of columns required to evaluate this node.

referencedFunctions

Returns a set of all functions which are used in this expression.

referencedVariables

Returns a set of all variables which are used in this expression.

Attributes

ntBinaryOperator

ntColumnRef

ntCondition

ntFunction

ntInOperator

ntIndexOperator

ntLiteral

ntUnaryOperator

qgis.core.QgsExpressionNode.parserFirstColumn

qgis.core.QgsExpressionNode.parserFirstLine

qgis.core.QgsExpressionNode.parserLastColumn

qgis.core.QgsExpressionNode.parserLastLine

class NamedNode(name: str, node: QgsExpressionNode)

Bases: sip.wrapper

Constructor for NamedNode

Parameters

QgsExpressionNode.NamedNode(QgsExpressionNode.NamedNode)

name
node
class NodeList

Bases: sip.wrapper

A list of expression nodes.

append(self, node: QgsExpressionNode)

Takes ownership of the provided node

append(self, node: QgsExpressionNode.NamedNode) Adds a named node. Takes ownership of the provided node.

New in version 2.16.

Parameters

node (QgsExpressionNode) –

at(self, i: int) → QgsExpressionNode

Gets the node at position i in the list.

New in version 3.0.

Parameters

i (int) –

Return type

QgsExpressionNode

clone(self) → QgsExpressionNode.NodeList

Creates a deep copy of this list. Ownership is transferred to the caller

Return type

QgsExpressionNode.NodeList

count(self) → int

Returns the number of nodes in the list.

Return type

int

dump(self) → str

Returns a string dump of the expression node.

Return type

str

hasNamedNodes(self) → bool

Returns True if list contains any named nodes

New in version 2.16.

Return type

bool

list(self) → List[QgsExpressionNode]

Gets a list of all the nodes.

Return type

List[QgsExpressionNode]

names(self) → List[str]

Returns a list of names for nodes. Unnamed nodes will be indicated by an empty string in the list.

New in version 2.16.

Return type

List[str]

class NodeType

Bases: int

clone(self) → QgsExpressionNode

Generate a clone of this node. Ownership is transferred to the caller.

Return type

QgsExpressionNode

Returns

a deep copy of this node.

dump(self) → str

Dump this node into a serialized (part) of an expression. The returned expression does not necessarily literally match the original expression, it’s just guaranteed to behave the same way.

Return type

str

eval(self, parent: QgsExpression, context: QgsExpressionContext) → Any

Evaluate this node with the given context and parent. This will return a cached value if it has been determined to be static during the prepare() execution.

New in version 2.12.

Parameters
Return type

Any

isStatic(self, parent: QgsExpression, context: QgsExpressionContext) → bool

Returns True if this node can be evaluated for a static value. This is used during the prepare() step and in case it returns True, the value of this node will already be evaluated and the result cached (and therefore not re-evaluated in subsequent calls to eval()). In case this returns True, prepareNode() will never be called.

New in version 3.0.

Parameters
Return type

bool

needsGeometry(self) → bool

Abstract virtual method which returns if the geometry is required to evaluate this expression.

This needs to call needsGeometry() recursively on any child nodes.

Return type

bool

Returns

True if a geometry is required to evaluate this expression

nodeType(self) → QgsExpressionNode.NodeType

Gets the type of this node.

Return type

QgsExpressionNode.NodeType

Returns

The type of this node

ntBinaryOperator = 1
ntColumnRef = 5
ntCondition = 6
ntFunction = 3
ntInOperator = 2
ntIndexOperator = 7
ntLiteral = 4
ntUnaryOperator = 0
parserFirstColumn
parserFirstLine
parserLastColumn
parserLastLine
prepare(self, parent: QgsExpression, context: QgsExpressionContext) → bool

Prepare this node for evaluation. This will check if the node content is static and in this case cache the value. If it’s not static it will call prepareNode() to allow the node to do initialization work like for example resolving a column name to an attribute index.

New in version 2.12.

Parameters
Return type

bool

referencedColumns(self) → Set[str]

Abstract virtual method which returns a list of columns required to evaluate this node.

When reimplementing this, you need to return any column that is required to evaluate this node and in addition recursively collect all the columns required to evaluate child nodes.

Return type

Set[str]

Returns

A list of columns required to evaluate this expression

referencedFunctions(self) → Set[str]

Returns a set of all functions which are used in this expression.

Return type

Set[str]

referencedVariables(self) → Set[str]

Returns a set of all variables which are used in this expression.

Return type

Set[str]