Python ctypes BigEndianStructure

import ctypes

class Header_Decoder(ctypes.BigEndianStructure): # {
    _pack_ = 1
    _fields_ = [
        ('protocol_id', ctypes.c_uint8, 8),      # 1 byte:  byte 1,      bits 00-07
        ('segmentation', ctypes.c_uint8, 3),     # 3 bits:  byte 2,      bits 08-10
        ('transaction_type', ctypes.c_uint8, 5), # 5 bits:  byte 2,      bits 11-15
        ('packet_length', ctypes.c_uint32),      # 4 bytes: bytes 3-6,   bits 16-47
        ('checksum', ctypes.c_uint16),           # 2 bytes: bytes 7-8,   bits 48-63
    ]
# } Header_Decoder

HEADER_LENGHT_BYTES = ctypes.sizeof(Header_Decoder)

packet = b'\xFF\x10\x00\x00\x00\x0C\x00\xE3\x48\x65\x79\x21'

header = Header_Decoder.from_buffer_copy(packet[0 : 0 + HEADER_LENGHT_BYTES])

print("Protocol ID:", header.protocol_id)
print("Segmentation:", header.segmentation)
print("Transaction type:", header.transaction_type)
print("Checksum:", header.checksum)
print("Data:", packet[HEADER_LENGHT_BYTES : header.packet_length].decode('ascii'))