动态导入模块,然后从所述模块实例化具有特定基类的对象

Question

我正在写一个应用程序.没有花哨的GUI:s或任何东西,只是一个普通的旧控制台应用程序.这个应用程序,让我们称之为App,需要能够在启动时加载插件.所以,很自然地,我创建了一个继承的插件类:

class PluginBase(object):
    def on_load(self):
        pass
    def on_unload(self):
        pass
    def do_work(self, data):
        pass

想法是在启动时,App会遍历当前目录,包括子目录,搜索包含本身是其子类的类的模块PluginBase.

更多代码:

class PluginLoader(object):
    def __init__(self, path, cls):
        """ path=path to search (unused atm), cls=baseclass """
        self.path=path
    def search(self):
        for root, dirs, files in os.walk('.'):
            candidates = [fname for fname in files if fname.endswith('.py') \
                                    and not fname.startswith('__')]
        ## this only works if the modules happen to be in the current working dir
        ## that is not important now, i'll fix that later
        if candidates:
            basename = os.path.split(os.getcwd())[1]
            for c in candidates:
                modname = os.path.splitext(c)[0]
                modname = '{0}.{1}'.format(basename, modname)
                __import__(mod)
                module = sys.modules[mod]

在最后一行之后,search我想以某种方式a)找到新加载的模块中的所有类,b)检查这些类中的一个或多个是否是PluginBasec的子类(如果b)实例化那些/那些类并添加到App的已加载模块列表.

我尝试了各种各样的组合issubclass,然后是一段激烈的dir时间和大约一个小时的恐慌谷歌搜索.我确实在这里找到了类似的方法,我尝试了复制粘贴,但得到一个错误,说Python不支持按文件名导入,此时我有点失去了注意力,因此,这篇文章写的.

我在我的智慧结束,所有帮助赞赏.

Answer 1

您可能会执行以下操作：

for c in candidates:
    modname = os.path.splitext(c)[0]
    try:
        module=__import__(modname)   #<-- You can get the module this way
    except (ImportError,NotImplementedError):
        continue
    for cls in dir(module):          #<-- Loop over all objects in the module's namespace
        cls=getattr(module,cls)
        if (inspect.isclass(cls)                # Make sure it is a class 
            and inspect.getmodule(cls)==module  # Make sure it was defined in module, not just imported
            and issubclass(cls,base)):          # Make sure it is a subclass of base
            # print('found in {f}: {c}'.format(f=module.__name__,c=cls))
            classList.append(cls)

为了测试以上内容，我不得不稍微修改一下您的代码；以下是完整的脚本。

import sys
import inspect
import os

class PluginBase(object): pass

def search(base):
    for root, dirs, files in os.walk('.'):
        candidates = [fname for fname in files if fname.endswith('.py') 
                      and not fname.startswith('__')]
        classList=[]
        if candidates:
            for c in candidates:
                modname = os.path.splitext(c)[0]
                try:
                    module=__import__(modname)
                except (ImportError,NotImplementedError):
                    continue
                for cls in dir(module):
                    cls=getattr(module,cls)
                    if (inspect.isclass(cls)
                        and inspect.getmodule(cls)==module
                        and issubclass(cls,base)):
                        # print('found in {f}: {c}'.format(f=module.__name__,c=cls))
                        classList.append(cls)
        print(classList)

search(PluginBase)