json.dump throwing “TypeError: {…} is not JSON serializable”

If it's a set type,then turn the set into list before serializing, or use a custom default handler to do so:

def set_default(obj):
    if isinstance(obj, set):
        return list(obj)
    raise TypeError

result = json.dumps(yourdata, default=set_default)

If you want a dict type,Maybe it's not actually a dictionary; it's another mapping type that looks like a dictionary. Use type()to verify. Pass it to dict() to get a real dictionary from it.　　

def __init__(self, element):
    self.element = element

def execute(self):
    if isinstance(self.element, dict):
        self.__iterate()
    else:
        return

def __iterate(self):
    for key in self.element:
        if isinstance(self.element[key], <ClassName>):
            self.element[key] = str(self.element[key])

        node = NormalizeData(self.element[key])
        node.execute()