How to convert java byte[] to python string?

Question

I know that java and python handle bytes differently so I am a little bit confused about how to convert byte[] to python string I have this byte[] in java

{ 118, -86, -46, -63, 100, -69, -30, -102, -82, -44, -40, 92, 0, 98, 36, -94 }

I want to convert it to python string here is how i did it

b=[118, -86, -46, -63, 100, -69, -30, -102, -82, -44, -40, 92, 0, 98, 36, -94]
str=""
for i in b:
    str=str+chr(abs(i))

But I am not really sure if this is the correct way to do it.

Answer 1

The Java byte type is a signed integer; the value ranges between -128 and 127. Python's chr expects a value between 0 and 255 instead. From the Primitive Data Types section of the Java tutorial:

byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive).

You need to convert from 2s compliment to an unsigned integer:

def twoscomplement_to_unsigned(i):
    return i % 256

result = ''.join([chr(twoscomplement_to_unsigned(i)) for i in b])

However, if this is Python 3, you really want to use the bytes type:

result = bytes(map(twoscomplement_to_unsigned, b))

Answer 2

Assuming you're using Python 3, bytes can already be initialized from a list. You'll need to convert the signed integers to unsigned bytes first.

items = [118, -86, -46, -63, 100, -69, -30, -102, -82, -44, -40, 92, 0, 98, 36, -94]
data = bytes(b % 256 for b in items)
print(data)  # b'v\xaa\xd2\xc1d\xbb\xe2\x9a\xae\xd4\xd8\\\x00b$\xa2'

If the bytes represent text, decode it afterwards. In your example, they do not represent text encoded to UTF-8, so this would fail.

data = data.decode('utf8')
print(data)