python - 动态导入的模块认为它没有类

Question

设置:Python 3.3

我正在创建一个应用程序，该应用程序在名为“sources”的文件夹中查找 .py 文件，并在其中查找扩展我定义的名为“SourceBase”的类的类。如果它们扩展了 SourceBase，我想创建一个新的类实例来处理。

我通过以下帖子做了相当多的研究，我了解其中的大部分内容:

• Dynamic importing of modules followed by instantiation of objects with a certain baseclass from said modules
• How to dynamically load a Python class
• Dynamic loading of python modules

我的文件夹设置是这样的，我相信这是相关的:

EPDownloader [package]
\
 epdownloader.py [main]
 SourceBase.py [contains SourceBase class]
 imageutils.py [this class will find and dynamically load the classes in the sources package]
 sources [package]
 \
  source1.py [has class that extends SourceBase]
  source2.py
  ...other plugins here...

我的问题是，我正在使用以下代码(来 self 上面列出的其他堆栈溢出问题)，并且它正在我的模块中搜索类，但它找不到我的类。它只是跳过它们。我不确定出了什么问题。这是我执行搜索的代码(它基于我发布的第一个链接):

<!--language: python-->
def getSources(self):
    pluginbase=SourceBase.SourceBase
    searchpath='sources'
    #We want to iterate over all modules in  the sources/ directory, allowing the user to make their own.
    for root, dirs, files in os.walk('./'+searchpath):
        print('files: ',files)
        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]
                print('importing: ',modname)
                module=__import__(searchpath+'.'+modname)   #<-- You can get the module this way
                print('Parsing module '+modname)
                for cls in dir(module):          #<-- Loop over all objects in the module's namespace
                    print('Inspecting item from module: '+str(cls))
                    cls=getattr(module,cls) #this seems to still be a module when it hits source1
                    print('Get attribute: '+str(cls))
                    if (inspect.isclass(cls)):                # Make sure it is a class
                        print('...is a class') 
                        if inspect.getmodule(cls)==module:  # Make sure it was defined in module, not just imported
                            print('...is in a module')
                            if issubclass(cls,pluginbase):          # Make sure it is a subclass of base
                                print('...subclasses '+pluginbase.__name__)
                                classList.append(cls)
        print(classList)

这是它给我的相关输出(我修剪了该代码输出的许多其他内容):

Inspecting item from module: source1
Get attribute: <module 'sources.source1' from    '/Users/Mgamerz/Documents/workspace/code/EPDownloader/sources/source1.py'>
[] <--- signifies it failed to find the source class

我很确定我的子类化有效，这是该类的片段:

from EPDownloader import SourceBase
class source1(SourceBase.SourceBase):
    def __init__(self):
        pass

我被这个问题难住了。我在这上面花了几个小时，但我不知道该怎么办。我有一种感觉，这是一个我没有看到的简单修复。有人可以帮我找到这里的错误吗？

[注意:我浏览了 StackOverflow 格式化帮助，没有看到任何格式化“突出显示”的方法，即在文本上放置灰色背景的方式，但是是内联的。这将有助于突出显示我试图传达的这个问题的部分内容。]

Answer 1

查看文档:http://docs.python.org/3.1/library/functions.html#import

When the name variable is of the form package.module, normally, the top-level package (the name up till the first dot) is returned, not the module named by name. However, when a non-empty fromlist argument is given, the module named by name is returned.

简单地替换

module=__import__(searchpath+'.'+modname)

与

module=__import__(searchpath+'.'+modname, None, None, "*")

它与“fromsources.source1 import *”相同，它告诉__import__获取给定模块内部的所有内容。