docs: def modify_attached_policies(self, role_name, new_policies):
          """Make sure this role has just the new policies"""
          parts = role_name.split('/', 1)
          if len(parts) == 2:
              prefix, name = parts
              prefix = "/{0}/".format(prefix)
          else:
              prefix = "/"
              name = parts[0]
  
          current_attached_policies = []
          with self.ignore_missing():
              current_attached_policies = self.client.list_attached_role_policies(RoleName=name)
              current_attached_policies = [p['PolicyArn'] for p in current_attached_policies["AttachedPolicies"]]
  
          new_attached_policies = ["arn:aws:iam::aws:policy/{0}".format(p) for p in new_policies]
  
          changes = list(Differ.compare_two_documents(current_attached_policies, new_attached_policies))
          if changes:
              with self.catch_boto_400("Couldn't modify attached policies", role=role_name):
                  for policy in new_attached_policies:
                      if policy not in current_attached_policies:
                          for _ in self.change("+", "attached_policy", role=role_name, policy=policy):
                              self.client.attach_role_policy(RoleName=name, PolicyArn=policy)
  
                  for policy in current_attached_policies:
                      if policy not in new_attached_policies:
                          for _ in self.change("-", "attached_policy", role=role_name, changes=changes, policy=policy):
                              self.client.detach_role_policy(RoleName=name, PolicyArn=policy)