How to use the rbtools.commands.CommandError function in RBTools

else:
                    raise CommandError(
                        'Unable to verify authenticity of file downloaded '
                        'from %s:\n%s' % (url, errors))
            finally:
                os.unlink(sig_filename)
        else:
            logging.info('"gpg" not installed. Skipping signature validation.')

            try:
                sha_url = '%s.sha256sum' % url
                logging.debug('Downloading %s', sha_url)
                response = urlopen(sha_url)
                real_sha = response.read().split(' ')[0]
            except (HTTPError, URLError) as e:
                raise CommandError('Error when downloading file: %s' % e)

            with open(zip_filename, 'rb') as f:
                our_sha = hashlib.sha256(f.read()).hexdigest()

            if real_sha == our_sha:
                logging.debug('Verified SHA256 hash')
            else:
                logging.debug('SHA256 hash does not match!')
                logging.debug('  Downloaded file hash was: %s', our_sha)
                logging.debug('  Expected hash was: %s', real_sha)

                raise CommandError(
                    'Unable to verify the checksum of the downloaded copy of '
                    '%s.\n'
                    'This could be due to an invasive proxy or an attempted '
                    'man-in-the-middle attack.' % url)

def main(self, *args):
        """Print the diff to terminal."""
        # The 'args' tuple must be made into a list for some of the
        # SCM Clients code. See comment in post.
        args = list(args)

        if self.options.revision_range:
            raise CommandError(
                'The --revision-range argument has been removed. To create a '
                'diff for one or more specific revisions, pass those '
                'revisions as arguments. For more information, see the '
                'RBTools 0.6 Release Notes.')

        if self.options.svn_changelist:
            raise CommandError(
                'The --svn-changelist argument has been removed. To use a '
                'Subversion changelist, pass the changelist name as an '
                'additional argument after the command.')

        repository_info, tool = self.initialize_scm_tool(
            client_name=self.options.repository_type)
        server_url = self.get_server_url(repository_info, tool)
        api_client, api_root = self.get_api(server_url)
        self.setup_tool(tool, api_root=api_root)

        try:
            revisions = tool.parse_revision_spec(args)
            extra_args = None
        except InvalidRevisionSpecError:
            if not tool.supports_diff_extra_args:
                raise

def no_commit_error(self):
        raise CommandError('No existing commit to stamp on.')

if not self.options.diff_filename:
            # If the user has requested to guess the summary or description,
            # get the commit message and override the summary and description
            # options.
            self.check_guess_fields()

        if self.options.update:
            self.options.rid = guess_existing_review_request_id(
                repository_info, self.options.repository_name, api_root,
                api_client, self.tool, self.cmd_args, guess_summary=False,
                guess_description=False,
                is_fuzzy_match_func=self._ask_review_request_match)

            if not self.options.rid:
                raise CommandError('Could not determine the existing review '
                                   'request to update.')

        # If only certain files within a commit are being submitted for review,
        # do not include the commit id. This prevents conflicts if mutliple
        # files from the same commit are posted for review separately.
        if self.options.include_files:
            commit_id = None

        request_id, review_url = self.post_request(
            repository_info,
            repository,
            server_url,
            api_root,
            self.options.rid,
            changenum=changenum,
            diff_content=diff,

if self.options.revision_range:
            raise CommandError(
                'The --revision-range argument has been removed. To post a '
                'diff for one or more specific revisions, pass those '
                'revisions as arguments. For more information, see the '
                'RBTools 0.6 Release Notes.')

        if self.options.svn_changelist:
            raise CommandError(
                'The --svn-changelist argument has been removed. To use a '
                'Subversion changelist, pass the changelist name as an '
                'additional argument after the command.')

        # Only one of --description and --description-file can be used
        if self.options.description and self.options.description_file:
            raise CommandError('The --description and --description-file '
                               'options are mutually exclusive.\n')

        # If --description-file is used, read that file
        if self.options.description_file:
            if os.path.exists(self.options.description_file):
                with open(self.options.description_file, 'r') as fp:
                    self.options.description = fp.read()
            else:
                raise CommandError(
                    'The description file %s does not exist.\n' %
                    self.options.description_file)

        # Only one of --testing-done and --testing-done-file can be used
        if self.options.testing_done and self.options.testing_file:
            raise CommandError('The --testing-done and --testing-done-file '
                               'options are mutually exclusive.\n')

try:
                review_request = guess_existing_review_request(
                    repository_info=repository_info,
                    repository_name=self.options.repository_name,
                    api_root=api_root,
                    api_client=api_client,
                    tool=self.tool,
                    revisions=get_revisions(self.tool, self.cmd_args),
                    guess_summary=False,
                    guess_description=False,
                    is_fuzzy_match_func=self._ask_review_request_match)
            except ValueError as e:
                raise CommandError(six.text_type(e))

            if not review_request or not review_request.id:
                raise CommandError('Could not determine the existing review '
                                   'request URL to land.')

            review_request_id = review_request.id
            is_local = True

        try:
            review_request = api_root.get_review_request(
                review_request_id=review_request_id)
        except APIError as e:
            raise CommandError('Error getting review request %s: %s'
                               % (review_request_id, e))

        if self.options.is_local is not None:
            is_local = self.options.is_local

        if is_local:

% (source_branch, destination_branch))
            else:
                print('Merging branch "%s" into "%s".'
                      % (source_branch, destination_branch))

            if not dry_run:
                try:
                    self.tool.merge(target=source_branch,
                                    destination=destination_branch,
                                    message=review_commit_message,
                                    author=author,
                                    squash=squash,
                                    run_editor=edit,
                                    close_branch=delete_branch)
                except MergeError as e:
                    raise CommandError(six.text_type(e))
        else:
            print('Applying patch from review request %s.' % review_request.id)

            if not dry_run:
                self.patch(review_request.id)

        print('Review request %s has landed on "%s".' %
              (review_request.id, self.options.destination_branch))

def post_process_options(self):
        # -g implies --guess-summary and --guess-description
        if self.options.guess_fields:
            self.options.guess_fields = self.normalize_guess_value(
                self.options.guess_fields, '--guess-fields')

            self.options.guess_summary = self.options.guess_fields
            self.options.guess_description = self.options.guess_fields

        if self.options.revision_range:
            raise CommandError(
                'The --revision-range argument has been removed. To post a '
                'diff for one or more specific revisions, pass those '
                'revisions as arguments. For more information, see the '
                'RBTools 0.6 Release Notes.')

        if self.options.svn_changelist:
            raise CommandError(
                'The --svn-changelist argument has been removed. To use a '
                'Subversion changelist, pass the changelist name as an '
                'additional argument after the command.')

        # Only one of --description and --description-file can be used
        if self.options.description and self.options.description_file:
            raise CommandError('The --description and --description-file '
                               'options are mutually exclusive.\n')

u'this review request\n')
                elif e.error_code == 219:
                    error_msg.append(
                        u'The generated diff file was empty. This '
                        u'usually means no files were\n'
                        u'modified in this change.\n')
                else:
                    error_msg.append(str(e).decode('utf-8') + u'\n')

                error_msg.append(
                    u'Your review request still exists, but the diff is '
                    u'not attached.\n')

                error_msg.append(u'%s\n' % review_request.absolute_url)

                raise CommandError(u'\n'.join(error_msg))

        try:
            draft = review_request.get_draft()
        except APIError as e:
            raise CommandError('Error retrieving review request draft: %s' % e)

        # Update the review request draft fields based on options set
        # by the user, or configuration.
        update_fields = {}

        if self.options.target_groups:
            update_fields['target_groups'] = self.options.target_groups

        if self.options.target_people:
            update_fields['target_people'] = self.options.target_people

"""Patch a single review request's diff using rbt patch."""
        patch_command = [RB_MAIN, 'patch']
        patch_command.extend(build_rbtools_cmd_argv(self.options))

        if self.options.edit:
            patch_command.append('-c')
        else:
            patch_command.append('-C')

        patch_command.append(six.text_type(review_request_id))

        rc, output = execute(patch_command, ignore_errors=True,
                             return_error_code=True)

        if rc:
            raise CommandError('Failed to execute "rbt patch":\n%s'
                               % output)