How to create objects on the fly in python?

You can use built-in type function:

testobj = type('testclass', (object,), 
                 {'test':[a1,a2,b2], 'test2':'something else', 'test3':1})()

But in this specific case (data object for Django templates), you should use @Xion's solution.

In Django templates, the dot notation (testobj.test) can resolve to the Python's [] operator. This means that all you need is an ordinary dict:

testobj = {'test':[a1,a2,b2], 'test2':'something else', 'test3':1}

Pass it as testobj variable to your template and you can freely use {{ testobj.test }} and similar expressions inside your template. They will be translated to testobj['test']. No dedicated class is needed here.