use bytearray instead of bytes to avoiding copying the data.

[kylinzzx]

I find the labrad system takes a long time transfer a large packet, which is noted in the issue #220. With the same test written by @maffoo , I test this new packetStream, with the following code.

def setting_time(n, cxn, server='manager'):
    s = bytes(bytearray(n))
    ti = time.time()
    cxn[server].echo(s)
    te = time.time()
    return te - ti
def main()
    print("Manager: ")
    with labrad.connect() as cxn:
        for x in range(20, 30):
            print(x, setting_time(2**x, cxn))
    print("Test Server: ")
    with labrad.connect() as cxn:
        for x in range(20, 30):
            print(x, setting_time(2**x, cxn, server='python_test_server'))
main()

Here is the result:

Manager:               
20 0.02391362190246582 
21 0.02747058868408203 
22 0.06482601165771484 
23 0.10375523567199707 
24 0.19747138023376465 
25 0.40491795539855957 
26 0.8242068290710449  
27 1.6051926612854004  
28 3.589486837387085   
29 10.249689817428589  
Test Server:           
20 0.04089021682739258 
21 0.1296536922454834  
22 0.11968016624450684 
23 0.21642041206359863 
24 0.4168851375579834  
25 1.0563695430755615  
26 1.7875730991363525  
27 4.136369943618774   
28 9.051634311676025   
29 17.714696407318115  

The old packetStream (using bytes) (only to 2**26, as it takes too much time)

Manager:                
20 0.019945859909057617 
21 0.03984975814819336  
22 0.11771774291992188  
23 0.530127763748169    
24 1.2997245788574219   
25 5.040466547012329    
26 19.881891012191772   
Test Server:            
20 0.03687715530395508  
21 0.07280373573303223  
22 0.19045782089233398  
23 0.6843514442443848   
24 2.4629600048065186   
25 9.668785810470581    
26 37.53484034538269