执行python manage.py startapp system命令报错

报错内容：

TypeError: unsupported operand type(s) for /: 'str' and 'str'

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(py3.7) C:\Users\klsml\Desktop\常用文件\py_learn\django_mall>python manage.py startapp system

Traceback (most recent call last):

  File "manage.py", line 22, in <module>

    execute_from_command_line(sys.argv)

  File "C:\Users\klsml\envs\py3.7-FwvP4-65\lib\site-packages\django\core\management\__init__.py", line 364, i

n execute_from_command_line

    utility.execute()

  File "C:\Users\klsml\envs\py3.7-FwvP4-65\lib\site-packages\django\core\management\__init__.py", line 308, i

n execute

    settings.INSTALLED_APPS

  File "C:\Users\klsml\envs\py3.7-FwvP4-65\lib\site-packages\django\conf\__init__.py", line 56, in __getattr_

_

    self._setup(name)

  File "C:\Users\klsml\envs\py3.7-FwvP4-65\lib\site-packages\django\conf\__init__.py", line 41, in _setup

    self._wrapped = Settings(settings_module)

  File "C:\Users\klsml\envs\py3.7-FwvP4-65\lib\site-packages\django\conf\__init__.py", line 110, in __init__

    mod = importlib.import_module(self.SETTINGS_MODULE)

  File "C:\Users\klsml\envs\py3.7-FwvP4-65\lib\importlib\__init__.py", line 127, in import_module

    return _bootstrap._gcd_import(name[level:], package, level)

  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import

  File "<frozen importlib._bootstrap>", line 983, in _find_and_load

  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked

  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked

  File "<frozen importlib._bootstrap_external>", line 728, in exec_module

  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed

  File "C:\Users\klsml\Desktop\常用文件\py_learn\django_mall\django_mall\settings.py", line 57, in <module>

    'DIRS': [BASE_DIR / 'templates']

TypeError: unsupported operand type(s) for /: 'str' and 'str'

百度查不到想要的结果，也不知道从何下手，请老师帮助，谢谢