varables = ["signal"]

# code ......
            self.signals[vt_symbol] = {
                "contract_size": contract_size,
                "target": 0,
                "factor": {
                    "entry_up": 0.0,
                    "entry_down": 0.0,
                    "exit_up": 0.0,
                    "exit_down": 0.0,
                    "n": 0.0,
                    "long_entry": 0.0,
                    "short_entry": 0.0,
                    "target": 0,
                    "traded": False,
                    "am": ArrayManager(size=20),
                    "bg": DailyBarGenerator(self.on_daily_bar, time(14, 59))
                }
            }

Traceback (most recent call last):
  File "C:\veighna_studio\lib\site-packages\vnpy_portfoliostrategy\ui\widget.py", line 258, in stop_strategy
    self.strategy_engine.stop_strategy(self.strategy_name)
  File "C:\veighna_studio\lib\site-packages\vnpy_portfoliostrategy\engine.py", line 445, in stop_strategy
    self.sync_strategy_data(strategy)
  File "C:\veighna_studio\lib\site-packages\vnpy_portfoliostrategy\engine.py", line 522, in sync_strategy_data
    save_json(self.data_filename, self.strategy_data)
  File "C:\veighna_studio\lib\site-packages\vnpy\trader\utility.py", line 119, in save_json
    json.dump(
  File "C:\veighna_studio\lib\json\__init__.py", line 179, in dump
    for chunk in iterable:
  File "C:\veighna_studio\lib\json\encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "C:\veighna_studio\lib\json\encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "C:\veighna_studio\lib\json\encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "C:\veighna_studio\lib\json\encoder.py", line 405, in _iterencode_dict
    yield from chunks
  [Previous line repeated 2 more times]
  File "C:\veighna_studio\lib\json\encoder.py", line 438, in _iterencode
    o = _default(o)
  File "C:\veighna_studio\lib\json\encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type ArrayManager is not JSON serializable