<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def pop(queue, quantity=1, backend='sqlite', is_runner=False):
    '''
    Pop one or more or all items from a queue

    CLI Example:

    .. code-block:: bash

        salt-run queue.pop myqueue
        salt-run queue.pop myqueue 6
        salt-run queue.pop myqueue all
        salt-run queue.pop myqueue 6 backend=sqlite
        salt-run queue.pop myqueue all backend=sqlite
    '''
    queue_funcs = salt.loader.queues(__opts__)
    cmd = '{0}.pop'.format(backend)
    if cmd not in queue_funcs:
        raise SaltInvocationError('Function "{0}" is not available'.format(cmd))
    ret = queue_funcs[cmd](quantity=quantity, queue=queue, is_runner=is_runner)
    return ret