示例
调用方法
class CorsMiddleware:
def process(self):
print('from auth.cors.CorsMiddleware.process')
cors.py
import importlib path = 'auth.cors.CorsMiddleware'
module_path, class_name = path.rsplit('.', maxsplit=1)
module = importlib.import_module(module_path)
cls = getattr(module, class_name)
obj = cls()
obj.process() # from auth.cors.CorsMiddleware.process
test.py
获取静态字段
class Dev:
DEBUG = True
settings.py
import importlib path = 'settings.Dev'
module_path, class_name = path.rsplit('.', maxsplit=1)
module = importlib.import_module(module_path)
cls = getattr(module, class_name)
for key in dir(cls):
if key.isupper():
print(getattr(cls,key)) # True
test.py
源码
其实很多在配置文件中通过类路径配置类的操作都是这样实现的，例如 Django 中在执行 wsgi 模块时加载配置文件：
def load_middleware(self):
self._request_middleware = []
self._view_middleware = []
self._template_response_middleware = []
self._response_middleware = []
self._exception_middleware = [] if settings.MIDDLEWARE is None:
warnings.warn(
"Old-style middleware using settings.MIDDLEWARE_CLASSES is "
"deprecated. Update your middleware and use settings.MIDDLEWARE "
"instead.", RemovedInDjango20Warning
)
handler = convert_exception_to_response(self._legacy_get_response)
for middleware_path in settings.MIDDLEWARE_CLASSES:
mw_class = import_string(middleware_path)
try:
mw_instance = mw_class()
except MiddlewareNotUsed as exc:
if settings.DEBUG:
if six.text_type(exc):
logger.debug('MiddlewareNotUsed(%r): %s', middleware_path, exc)
else:
logger.debug('MiddlewareNotUsed: %r', middleware_path)
continue if hasattr(mw_instance, 'process_request'):
self._request_middleware.append(mw_instance.process_request)
if hasattr(mw_instance, 'process_view'):
self._view_middleware.append(mw_instance.process_view)
if hasattr(mw_instance, 'process_template_response'):
self._template_response_middleware.insert(0, mw_instance.process_template_response)
if hasattr(mw_instance, 'process_response'):
self._response_middleware.insert(0, mw_instance.process_response)
if hasattr(mw_instance, 'process_exception'):
self._exception_middleware.insert(0, mw_instance.process_exception)
else:
handler = convert_exception_to_response(self._get_response)
for middleware_path in reversed(settings.MIDDLEWARE):
middleware = import_string(middleware_path)
try:
mw_instance = middleware(handler)
except MiddlewareNotUsed as exc:
if settings.DEBUG:
if six.text_type(exc):
logger.debug('MiddlewareNotUsed(%r): %s', middleware_path, exc)
else:
logger.debug('MiddlewareNotUsed: %r', middleware_path)
continue if mw_instance is None:
raise ImproperlyConfigured(
'Middleware factory %s returned None.' % middleware_path
) if hasattr(mw_instance, 'process_view'):
self._view_middleware.insert(0, mw_instance.process_view)
if hasattr(mw_instance, 'process_template_response'):
self._template_response_middleware.append(mw_instance.process_template_response)
if hasattr(mw_instance, 'process_exception'):
self._exception_middleware.append(mw_instance.process_exception) handler = convert_exception_to_response(mw_instance)
self._middleware_chain = handler
django.core.handlers.base.BaseHandler.load_middleware
def import_string(dotted_path):
"""
Import a dotted module path and return the attribute/class designated by the
last name in the path. Raise ImportError if the import failed.
"""
try:
module_path, class_name = dotted_path.rsplit('.', 1)
except ValueError:
msg = "%s doesn't look like a module path" % dotted_path
six.reraise(ImportError, ImportError(msg), sys.exc_info()[2]) module = import_module(module_path) try:
return getattr(module, class_name)
except AttributeError:
msg = 'Module "%s" does not define a "%s" attribute/class' % (
module_path, class_name)
six.reraise(ImportError, ImportError(msg), sys.exc_info()[2])
django.utils.module_loading.import_string