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.

Signals

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:
  • name – node name
  • node – node

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.

at(self, i: int) → QgsExpressionNode

Gets the node at position i in the list.

New in version 3.0.

clone(self) → QgsExpressionNode.NodeList

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

count(self) → int

Returns the number of nodes in the list.

dump(self) → str

Returns a string dump of the expression node.

hasNamedNodes(self) → bool

Returns true if list contains any named nodes

New in version 2.16.

list(self) → object

Gets a list of all the nodes.

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.

class NodeType

Bases: int

clone(self) → QgsExpressionNode

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

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.

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.

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.

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.

Returns:true if a geometry is required to evaluate this expression
nodeType(self) → QgsExpressionNode.NodeType

Gets the type of this node.

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.

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.

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.

referencedVariables(self) → Set[str]

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