Python join on byte array

Question

I need to loop through an array of byte arrays and then select a matching element from a dictionary. However my attempt to join the byte array fails:

roms = {
  "\xff\xfe\x88\x84\x16\x03\xd1":"living_room",
  "\x10\xe5x\xd5\x01\x08\x007":"bed_room"
}

devices = [bytearray(b'(\xff\xfe\x88\x84\x16\x03\xd1'), bytearray(b'\x10\xe5x\xd5\x01\x08\x007')]
for device in devices:
  DEV = "".join(device)
  print(roms[DEV])

>> TypeError: sequence item 0: expected str instance, int found

So it appears that you can't join an integer, is there another way?

UPDATE 1

With much help and patience from @falsetrue, I have managed to join the array. However the resulting string still throws a key error when I attempt to get the devices dictionary item:

roms = {
  "\xff\xfe\x88\x84\x16\x03\xd1":"living_room",
  "\x10\xe5x\xd5\x01\x08\x007":"bed_room"
}

devices = [bytearray(b'(\xff\xfe\x88\x84\x16\x03\xd1'), bytearray(b'\x10\xe5x\xd5\x01\x08\x007')]

for device in devices:
  DEV = str(bytes(device)).strip('b').strip("'").strip('(') # > this results in: \xff\xfe\x88\x84\x16\x03\xd1 - but still gives keyError
  #DEV = bytes(device).lstrip(b'(') # > This results in: b'\xff\xfe\x88\x84\x16\x03\xd1' - keyError
  print(DEV)
  print(roms["\xff\xfe\x88\x84\x16\x03\xd1"])
  print(roms[DEV])
  print()

>> \xff\xfe\x88\x84\x16\x03\xd1
>> living_room
>> KeyError: \xff\xfe\x88\x84\x16\x03\xd1

UPDATE 2

Here's the device info:

release='1.3.0.b1', 
version='v1.8.6-379-gc44ebac on 2017-01-13', 
machine='WiPy with ESP32'

Maybe someone else with a WIPY2 can verify this for me?

Sounds like an X-Y problem. There is no reason to "join" a byte array as you've shown it. You're not even joining two together. Please explain more. Also, shouldn't your keys in roms be bytes strings? For example: b'\xff\xfe...'. If they were, and devices were also byte strings, then roms[devce] would just work. — Mark Tolonen
– Mark Tolonen, Commented Jan 17, 2017 at 3:07
I didn't suggest to use str; it will add b'...' and escape bytes; It will make situtation worse; don't do that! — falsetru
– falsetru, Commented Jan 17, 2017 at 6:16
Just for reference, what version of Micropython is this - pyboard, WiPy, etc? — nekomatic
– nekomatic, Commented Jan 17, 2017 at 9:55
@nekomatic - 'WiPy', release='1.3.0.b1', version='v1.8.6-379-gc44ebac on 2017-01-13', machine='WiPy with ESP32' — crankshaft
– crankshaft, Commented Jan 17, 2017 at 9:59
OK, that's worth mentioning in any further questions. The original CC3200 based WiPy had a significantly cut-down version of MicroPython compared to the pyboard reference version, but it looks as if the ESP32 WiPy is closer to the reference. — nekomatic
– nekomatic, Commented Jan 17, 2017 at 10:11

falsetru · Accepted Answer · 2017-01-17 03:06:59Z

1

If you're using Python 3.x:

You can decode the bytes to str using bytes.decode (or bytearray.decode)

devices = [bytearray(b'\xff\xfe\x88\x84\x16\x03\xd1'),
           bytearray(b'\x10\xe5x\xd5\x01\x08\x007')]
for device in devices:
    DEV = device.decode('latin1')  # Use bytes.decode to convert to str
                                   # (or bytearray.decode)
    print(roms[DEV])

prints

living_room
bed_room

BTW, I removed ( in byte literal.

devices = [bytearray(b'(\xff\xfe\x88\x84\x16\x03\xd1'), ...
                       ^

UPDATE

If you're using Python 2.x:

Convert the device to bytes using bytes function:

for device in devices:
    DEV = bytes(device)
    print(roms[DEV])

edited Jan 17, 2017 at 3:06

answered Jan 17, 2017 at 2:54

falsetru

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14 Comments

crankshaft Over a year ago

Thanks so much for helping, but when I run that I get: "AttributeError: 'bytearray' object has no attribute 'decode'"

falsetru Over a year ago

@crankshaft, How about DEV = bytes(device).decode('latin1') ?

crankshaft Over a year ago

Made some progress, that line does not error, but when I try and use the DEV to get the dictionary device I get another error: "KeyError: (��"

falsetru Over a year ago

@crankshaft, I misunderstood you are using Python 3.x. I updated the answer, please check it out. In short, try DEV = bytes(device). micropython seems not fully implemented Python 3.x.

falsetru Over a year ago

@crankshaft, As I wrote in the answer, there is a extra ( in the bytearray literal. Was it intentional?

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