charms.reactive remote count

handlers.py

@when('rel.connected')
def handle_rel(rel):
    hookenv.log('There are {} remote units'.format(rel.remote_count()))

provides.py

class RelProvides(RelationBase):
    scope = scopes.UNIT

    @hook('{provides:rel}-relation-joined')
    def joined(self):
        self.set_state('{relation_name}.connected')
        
    def remote_count(self):
        return len(self.conversations())