human
Complete this python program:
def _invalidate_queue(q, val=None, sync=True):
assistant
#Here is the Python program you requested.

    """Breaks a Queue such that it never blocks, always has size 1,
    and has no maximum size. get()ing from the queue returns `val`,
    which defaults to None. `sync` controls whether a lock is
    required (because it\s not reentrant!).
    """
    def _qsize(len=len):
        return 1
    def _put(item):
        pass
    def _get():
        return val
    if sync:
        q.mutex.acquire()
    try:
        q.maxsize = 2
        q._qsize = _qsize
        q._put = _put
        q._get = _get
        q.not_empty.notifyAll()
        q.not_full.notifyAll()
    finally:
        if sync:
            q.mutex.release()