标签：ring ogg eve design let ast 使用 实现 prope
解析字符串，并导入改路径的模块
# 根据字符串导入模块 # 通畅用来导入包下面的模块 o = importlib.import_module("aa.bb") s2 = "Person" # 由字符串找函数、方法、类 利用 反射 the_class = getattr(o, "Person") p2 = the_class("小黑") p2.dream()
从"aa.bb"路径导入bb模块。
在Django源码目录"django/utils/module_loading.py",使用importlib中的import_module函数实现了Django中自定义的import_string(dotted_path)方法
源码：
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 as err: raise ImportError("%s doesn‘t look like a module path" % dotted_path) from err module = import_module(module_path) try: return getattr(module, class_name) except AttributeError as err: raise ImportError(‘Module "%s" does not define a "%s" attribute/class‘ % ( module_path, class_name) ) from err
解析：
例如Django项目settings.py中的‘django.middleware.clickjacking.XFrameOptionsMiddleware‘，在dotted_path.rsplit(‘.‘, 1)后生成元组(‘django.middleware.clickjacking‘,‘XFrameOptionsMiddleware‘),再使用import_module导入‘django.middleware.clickjacking‘模块，最后使用映射获取类XFrameOptionsMiddleware。
在"django\core\handlers\base.py"中class BaseHandler中有load_middleware()方法用来导入settings中的中间件，其中调用了上面的import_string()方法，源码如下：
def load_middleware(self): """ Populate middleware lists from settings.MIDDLEWARE. Must be called after the environment is fixed (see __call__ in subclasses). """ self._request_middleware = [] self._view_middleware = [] self._template_response_middleware = [] self._response_middleware = [] self._exception_middleware = [] 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 str(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) # We only assign to this when initialization is complete as it is used # as a flag for initialization being complete.
标签：ring ogg eve design let ast 使用 实现 prope
原文地址：https://www.cnblogs.com/bad-robot/p/9746870.html
