'Iterate over the mappings from all modules in the plugin manager.
Mappings are returned as a list of (key, value) tuples.'

def load_all(self, plugin_manager):

    mod_dicts = plugin_manager.map_to_modules(self.load_from_module)
    return itertools.chain.from_iterable((six.iteritems(d) for d in mod_dicts))
