from PySide2.QtCore import QObject, Property


class SomeObject(QObject):
    _value = 'ConstantValue'
    constantValue = Property(str, lambda self: self._value, constant=True)


obj = SomeObject()
metaObject = obj.metaObject()
# fails with PySide2 5.12, worked before
assert metaObject.property(metaObject.indexOfProperty("constantValue")).isConstant()