check if a bytes-array is a hex-literal

January 27, 2023

From an API I receive following types of bytes-array:

b'2021:09:30 08:28:24'

b'\x01\x02\x03\x00'

I know how to get the values for them, like for the first one with value.decode() and for the second one with ''.join([str(c) for c in value])

the problem is, I need to do this dynamically. I don’t know what the second one is called (is it a hex-literal?), but I can’t even check for value.decode().startswith('\x'), it gives me a

SyntaxError: (unicode error) ‘unicodeescape’ codec can’t decode bytes in position 0-1: truncated \xXX escape

which makes sense, because of the escape sequence.

so, I need something that checks, if the value is from format \x... or a simple string I can just use with decode().

>Solution :

Use a combination of try/except with isprintable():

def bytes_to_string(data):
    try:
        rv = data.decode()
        return rv if rv.isprintable() else data.hex()
    except UnicodeDecodeError:
        return data.hex()

print(bytes_to_string(b'\x01\x02\x03\x00'))    # Will decode but to unprintable string
print(bytes_to_string(b'2021:09:30 08:28:24')) # Will decode to printable string
print(bytes_to_string(b'Z\xfcrich'))           # Will throw an exception on decode