Python:使用type()时缺少类属性__module__？

Question

我正在尝试动态构造一些类,这些类是django的models.Model的子类.我的代码看起来像这样:

MyModel = type('MyModel', (models.Model,), {
    'field': models.BooleanField()
    })

当Django尝试加载它时,它会给出以下异常:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 88, in inner_run
    self.validate(display_num_errors=True)
  File "/usr/lib/python2.7/site-packages/django/core/management/base.py", line 249, in validate
    num_errors = get_validation_errors(s, app)
  File "/usr/lib/python2.7/site-packages/django/core/management/validation.py", line 36, in get_validation_errors
    for (app_name, error) in get_app_errors().items():
  File "/usr/lib/python2.7/site-packages/django/db/models/loading.py", line 146, in get_app_errors
    self._populate()
  File "/usr/lib/python2.7/site-packages/django/db/models/loading.py", line 61, in _populate
    self.load_app(app_name, True)
  File "/usr/lib/python2.7/site-packages/django/db/models/loading.py", line 78, in load_app
    models = import_module('.models', app_name)
  File "/usr/lib/python2.7/site-packages/django/utils/importlib.py", line 35, in import_module
    __import__(name)
  File "/home/user/project/app/models.py", line 221, in <module>
    'field': models.BooleanField()
  File "/usr/lib/python2.7/site-packages/django/db/models/base.py", line 38, in __new__
    module = attrs.pop('__module__')
KeyError: '__module__'

看起来像使用构造的类type()没有获得__module__为定义的类所呈现的成员class.这里发生了什么？

Answer 1

可能是元类是您需要的最佳选择而不是低级别type()？

但在大多数情况下,你可以使用__name__作为一个价值__module__像

MyModel = type('MyModel', (models.Model,), {
    'field': models.BooleanField(),
    '__module__': __name__,
})

Django使用__module__值来确定哪个django app拥有这个模型,因此模型my_app1/models.py将包含my_app1.models和django知道该文件模块中的模型属于my_app1应用程序.