python queue get size, use qsize() or len()?

For most containers, you'll want len, but Queue.Queue doesn't actually support len. This may be because it's old or because getting the length of a queue in a multithreaded environment isn't particularly useful. In any case, if you want the (approximate) size of a Queue, you want qsize.

queue.qsize() doesn't return the number of bytes in the queue. It returns the number of "things" placed in the queue.

If you put 5 byte-arrays of 100 bytes in the queue, the qsize() will be 5, not 500.