python 提供了如下两个函数来检查类型： issubclass(cls, class_or_tuple)：检查 cls 是否为后一个类或元组包含的多个类中任意类的子类。isinstance(obj, class_or_tuple)：检查 obj 是否为后一个类或元组包含的多个
we have the problem that ShowHelp seems to fail under Vista and Windows Server 2008 if the path name of the help file contains a virtualized folder name.
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