def freeze(h, output_yaml, resolve, groups):
    """Output installed packages."""
    if not groups:
        groups = filter(lambda group: not group.lower().startswith("bower"),
                        h.requirements.keys())
    else:
        groups = [text_type.strip(group) for group in groups.split(",")]

    if output_yaml:
        for requirements in h.requirements.values():
            for requirement in requirements:
                if resolve and not requirement.version:
                    requirement.load_installed_version()
        click.echo(h.requirements.yaml)
    else:
        for group in groups:
            if not h.requirements[group]:
                continue
            click.echo("# {}".format(group))
            for requirement in h.requirements[group]:
                if resolve and not requirement.version:
                    requirement.load_installed_version()
                click.echo(str(requirement))
def install_secret_key(app, filename='secret_key'):
    """Configure the SECRET_KEY from a file
    in the instance directory.

    If the file does not exist, print instructions
    to create it from a shell with a random key,
    then exit.
    """
    filename = os.path.join(app.instance_path, filename)

    try:
        app.config['SECRET_KEY'] = open(filename, 'rb').read()
    except IOError:
        print('Error: No secret key. Create it with:')
        full_path = os.path.dirname(filename)
        if not os.path.isdir(full_path):
            print('mkdir -p {filename}'.format(filename=full_path))
        print('head -c 24 /dev/urandom > {filename}'.format(filename=filename))
        sys.exit(1)