Converts a decimal value into a hex byte string

gen_byte_str

def gen_bytestr(dec_val, byte_str_len=4):
    """ takes dec_val, converts to hex and returns byte_str that is byte_str_len long 
        e.g. gen_bytestr(255, 4) -> '\x00\x00\x00\xff'
    """
    # first check if dec_val can even be represented by a byte string of byte_str_len length
    byte_count = (int.bit_length(dec_val) / 4)
    if byte_count > byte_str_len:
        raise Exception('[!] {val} too large for {max} byte length. (requires {req} bytes)'.format(
            val=dec_val, max=byte_str_len, req=byte_count))
    hex_val = hex(dec_val)
    hex_val = hex_val[2:]  # hex() prepends '0x' to val, strip it
    hex_val = hex_val.zfill(byte_str_len * 2)  # fill out with 0's to fit byte_str_len
    a_bytearray = bytearray.fromhex(hex_val)
    return a_bytearray