The difference between PythonExtension and ExtensionObject

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Hi, guys,
PyCXX is great. :)
After reading the code, I am not clear about the relationship between
PythonExtension and ExtensionObject.
Some usage in the sample code was

Py::ExtensionObject<range> rheap( new range(1, 10, 2) );

and

range is based on PythonExtension.


How to use ExtensionObject?

Thanks!