Import class from module dynamically

问题

I have class called 'my_class' placed in 'my_module'. And I need to import this class. I tried to do it like this:

import importlib
result = importlib.import_module('my_module.my_class')

but it says:

ImportError: No module named 'my_module.my_class'; 'my_module' is not a package

So. As I can see it works only for modules, but can't handle classes. How can I import a class from a module?

回答1:

It is expecting my_module to be a package containing a module named 'my_class'. If you need to import a class, or an attribute in general, dynamically, just use getattr after you import the module:

cls = getattr(import_module('my_module'), 'my_class')

Also, yes, it does only work with modules. Remember importlib.import_module is a wrapper of the internal importlib.__import__ function. It doesn't offer the same amount of functionality as the full import statement which, coupled with from, performs an attribute look-up on the imported module.

回答2:

import importlib
import logging

logger = logging.getLogger(__name__)


def factory(module_class_string, super_cls: type = None, **kwargs):
    """
    :param module_class_string: full name of the class to create an object of
    :param super_cls: expected super class for validity, None if bypass
    :param kwargs: parameters to pass
    :return:
    """
    module_name, class_name = module_class_string.rsplit(".", 1)
    module = importlib.import_module(module_name)
    assert hasattr(module, class_name), "class {} is not in {}".format(class_name, module_name)
    logger.debug('reading class {} from module {}'.format(class_name, module_name))
    cls = getattr(module, class_name)
    if super_cls is not None:
        assert issubclass(cls, super_cls), "class {} should inherit from {}".format(class_name, super_cls.__name__)
    logger.debug('initialising {} with params {}'.format(class_name, kwargs))
    obj = cls(**kwargs)
    return obj

来源：https://stackoverflow.com/questions/41678073/import-class-from-module-dynamically