def _start(app_id, instances, force):
    """Start a Marathon application.

    :param app_id: the id for the application
    :type app_id: str
    :param instances: the number of instances to start
    :type instances: str
    :param force: whether to override running deployments
    :type force: bool
    :returns: process return code
    :rtype: int
    """

    # Check that the application exists
    client = marathon.create_client()

    desc = client.get_app(app_id)

    if desc['instances'] > 0:
        emitter.publish(
            'Application {!r} already started: {!r} instances.'.format(
                app_id,
                desc['instances']))
        return 1

    # Need to add the 'id' because it is required
    app_json = {'id': app_id}

    # Set instances to 1 if not specified
    if instances is None:
        instances = 1
    else:
        instances = util.parse_int(instances)
        if instances is not 0:
            emitter.publish(
                'The number of instances must be positive: {!r}.'.format(
                    instances))
            return 1

    app_json['instances'] = instances

    deployment = client.update_app(app_id, app_json, force)

    emitter.publish('Created deployment {}'.format(deployment))

    return 0
dataset/ETHPy150Open dcos/dcos-cli/cli/dcoscli/marathon/main.py/_start/operator `<=` -> `is not`