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python-3.xdecodingunpack

unpacking a 4-byte class gives a unpacking error

I'm trying to decode a bytes object, and I'm getting an error, even though by object is a bytes class of 4 bytes.

what I'm calling:

struct.unpack('>f', reg_hex[2:10])[0]

If I print the value of reg_hex[2:10]:

print("reg_hex: {}".format(reg_hex[2:10]))

    reg_hex: b'3a8a1b45'

If I print the type of reg_hex[2:10]:

print("reg_hex: {}".format(type(reg_hex[2:10])))
    reg_hex: <class 'bytes'>

So reg_hex is a bytes class of 4 bytes, however struct.unpack doesn't seem to be happy with it.

Am I doing something wrong?

Solution

  • Those are 8 bytes, not 4. They're the characters 3, a, ... etc.

    You need first to convert from hex to actual bytes. For example:

    bindata = bytes(int(reg_hex[i:i+2], 16) for i in range(0, reg_hex(x), 2))