Walk a QgsExpression tree

walkexpressioon.py

def walk(node):
    if node.nodeType() == QgsExpression.ntBinaryOperator:
        handle_binary(node)
    elif node.nodeType() == QgsExpression.ntUnaryOperator:
        print("Unary")
    elif node.nodeType() == QgsExpression.ntInOperator:
        print("In")
    elif node.nodeType() == QgsExpression.ntFunction:
        handle_function(node)
    elif node.nodeType() == QgsExpression.ntLiteral:
        handle_literal(node)
    elif node.nodeType() == QgsExpression.ntColumnRef:
        print("ColumnRef")
    elif node.nodeType() == QgsExpression.ntCondition:
        print("Condition")

def handle_binary(node):
    print("BINARY")
    op = node.op()
    ops = [
        "OR", "AND",
        "=", "<>", "<=", ">=", "<", ">", "~", "LIKE", "NOT LIKE", "ILIKE", "NOT ILIKE", "IS", "IS NOT",
        "+", "-", "*", "/", "//", "%", "^",
        "||"
    ]
    left = node.opLeft()
    right = node.opRight()
    walk(left)
    print(ops[op])
    walk(right)

def handle_literal(node):
    print("LITERAL")
    print("Value:" + str(node.value()))

def handle_function(node):
    print("FUNCTION")
    fnIndex = node.fnIndex()
    func = QgsExpression.Functions()[fnIndex]
    args = node.args().list()
    print(func.name())
    for arg in args:
        walk(arg)

exp = QgsExpression("1 = 2")
walk(exp.rootNode())

exp = QgsExpression("to_string(1 + 2)")
walk(exp.rootNode())