python中importlib模块安装_python之importlib模块

1、import_module方法

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。

2、import_module在Django中的使用

2.1、Django中使用import_module实现import_string方法

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：

defimport_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)exceptValueError as err:raise ImportError("%s doesn't look like a module path" % dotted_path) fromerr

module=import_module(module_path)try:returngetattr(module, class_name)exceptAttributeError 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。

2.2、Django中使用import_string导入模块中的类

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：

defload_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 inreversed(settings.MIDDLEWARE):

middleware=import_string(middleware_path)try:

mw_instance=middleware(handler)exceptMiddlewareNotUsed as exc:ifsettings.DEBUG:ifstr(exc):

logger.debug('MiddlewareNotUsed(%r): %s', middleware_path, exc)else:

logger.debug('MiddlewareNotUsed: %r', middleware_path)continue

if mw_instance isNone:raiseImproperlyConfigured('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.