def register_function(self, function_name, function):
        """
        Register a function for the module.

        The following functions can be registered


            ..  py:function:: content_function()

            Called to discover what modules a container is displaying.  This is
            used to determine when updates need passing on to the container and
            also when modules can be put to sleep.

            the function must return a set of module names that are being
            displayed.

            .. note::

                This function should only be used by containers.

            ..  py:function:: urgent_function(module_names)

            This function will be called when one of the contents of a container
            has changed from a non-urgent to an urgent state.  It is used by the
            group module to switch to displaying the urgent module.

            ``module_names`` is a list of modules that have become urgent

            .. note::

                This function should only be used by containers.
        """
        my_info = self._get_module_info(self._module.module_full_name)
        my_info[function_name] = function

        Register a function for the module.

        The following functions can be registered


            ..  py:function:: content_function()

            Called to discover what modules a container is displaying.  This is
            used to determine when updates need passing on to the container and
            also when modules can be put to sleep.

            the function must return a set of module names that are being
            displayed.

            .. note::

                This function should only be used by containers.

            ..  py:function:: urgent_function(module_names)

            This function will be called when one of the contents of a container
            has changed from a non-urgent to an urgent state.  It is used by the
            group module to switch to displaying the urgent module.

            ``module_names`` is a list of modules that have become urgent

            .. note::

                This function should only be used by containers.
        
py3status/py3.py