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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 promote(self, cart_name):
 """ `name` - name of cart Promote a cart from its current environment to the next in the chain. """

        cart = juicer.common.Cart.Cart(cart_name=cart_name, autoload=True, autosync=True)
        old_env = cart.current_env
        cart.current_env = juicer.utils.get_next_environment(cart.current_env)

        # figure out what needs to be done to promote packages. If
        # packages are going between environments that are on the same
        # host and we don't need to sign them just associate with both
        # repos.
        if juicer.utils.env_same_host(old_env, cart.current_env) and (self.connectors[old_env].requires_signature == self.connectors[cart.current_env].requires_signature):
            juicer.utils.Log.log_info("Envs %s and %s exist on the same host, calling remote associate action" % (old_env, cart.current_env))
            juicer.utils.Log.log_info("Promoting %s from %s to %s" %
                    (cart_name, old_env, cart.current_env))
            # iterate through packages and associate to new repo
            for repo, items in cart.iterrepos():
                query = '/repositories/%s-%s/actions/associate/' % (repo, cart.current_env)
                for item in items:
                    source_repo_id = '%s-%s' % (repo, old_env)
                    data = {
                        'source_repo_id': str(source_repo_id),
                        'criteria': {
                            'type_ids': ['rpm'],
                            'filters': {
                                'unit': {
                                    'filename': str(item.path.split('/')[-1])
                                    }
                                }
                            }
                        }
                    _r = self.connectors[cart.current_env].post(query, data)
                    if _r.status_code != Constants.PULP_POST_ACCEPTED:
                        raise JuicerPulpError("Package association call was not accepted. Terminating!")
                    else:
                        # association was accepted so publish destination repo
                        con = self.connectors[cart.current_env]
                        con.post('/repositories/%s-%s/actions/publish/' % (repo, cart.current_env), {'id': 'yum_distributor'})
                        # also update the item's remote path
                        filename = item.path.split('/')[-1]
                        item.update('%s/%s' % (juicer.utils.pulp_repo_path(con, '%s-%s' % (repo, cart.current_env)), filename))
            # we didn't bomb out yet so let the user know what's up
            juicer.utils.Log.log_info("Package association calls were accepted. Trusting that your packages existed in %s" % old_env)
            # we can save and publish here because upload does this too...
            cart.save()
            self.publish(cart)
        else:
            juicer.utils.Log.log_debug("Syncing down rpms...")
            cart.sync_remotes()
            self.sign_cart_for_env_maybe(cart, cart.current_env)

            juicer.utils.Log.log_info("Promoting %s from %s to %s" %
                    (cart_name, old_env, cart.current_env))

            for repo in cart.repos():
                juicer.utils.Log.log_debug("Promoting %s to %s in %s" %
                                           (cart[repo], repo, cart.current_env))
            # reiterating that upload will save and publish the cart
            self.upload(cart.current_env, cart)