[FIXED] Why are my byte arrays not different even though print() says they are?

Issue

I am new to python so please forgive me if I'm asking a dumb question. In my function I generate a random byte array for a given number of bytes called "input_data", then I add bytewise some bit errors and store the result in another byte array called "output_data". The print function shows that it works exactly as expected, there are different bytes. But if I compare the byte arrays afterwards they seem to be identical!

def simulate_ber(packet_length, ber, verbose=False):
    # generate input data
    input_data = bytearray(random.getrandbits(8) for _ in xrange(packet_length))
    if(verbose):
        print(binascii.hexlify(input_data)+" <-- simulated input vector")

    output_data = input_data

    #add bit errors
    num_errors = 0
    for byte in range(len(input_data)):
        error_mask = 0
        for bit in range(0,7,1):
            if(random.uniform(0, 1)*100 < ber):
                error_mask |= 1 << bit
                num_errors += 1
        output_data[byte] = input_data[byte] ^ error_mask

    if(verbose):
        print(binascii.hexlify(output_data)+" <-- output vector")
        print("number of simulated bit errors: " + str(num_errors))

    if(input_data == output_data):
        print ("data identical")


number of packets: 1
bytes per packet: 16
simulated bit error rate: 5
start simulation...
0d3e896d61d50645e4e3fa648346091a <-- simulated input vector
0d3e896f61d51647e4e3fe648346001a <-- output vector
number of simulated bit errors: 6
data identical

Where is the bug? I am sure the problem is somewhere between my ears...

Thank you in advance for your help!

Solution

output_data = input_data

Python is a referential language. When you do the above, both variables now refer to the same object in memory. e.g:

>>> y=['Hello']
>>> x=y
>>> x.append('World!')
>>> x
['Hello', 'World!']
>>> y
['Hello', 'World!']

Cast output_data as a new bytearray and you should be good:

output_data = bytearray(input_data)

Answered By - Kind Stranger