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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def registerRti(self, fullName, fullClassName, extensions=None, pythonPath=''):
 """ Class that maintains the collection of registered inspector classes. Maintains a lit of file extensions that open the RTI by default. """

        check_is_a_sequence(extensions)
        extensions = extensions if extensions is not None else []
        extensions = [prepend_point_to_extension(ext) for ext in extensions]

        regRti = RtiRegItem(fullName, fullClassName, extensions, pythonPath=pythonPath)
        self.registerItem(regRti)