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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 activate(self, *, filter_func=None):
        '''
        Activate the type safety checker. After the call all functions
        that need to be checked will be.
        '''

        if self.active:
            raise RuntimeError("Type safety check already active")

        self.__module_finder = ModuleFinder(Validator.decorate)
        if filter_func is not None:
            self.__module_finder.set_filter(filter_func)
        self.__module_finder.install()