[Python] Using a pointer to fill a ctypes structure

I have need create a ctypes struct using a pointer. Example code

class MessageDecoder:
def __init__(self, raw_data : bytes):
self.raw_data = raw_data
self.writable_raw_data = None
self.datagram = None
self.tag = None

def decode(self):
c_array = cast(self.raw_data, POINTER(c_ubyte *
len(self.raw_data)))[0]
data_pointer = pointer(c_array)
self.datagram = Datagram.from_buffer(data_pointer)


I get the c_array. I can get the pointer. However, trying to create Datagram fails. I can create one using c_array. EX: Datagram.from_buffer(c_array) Datagram looks like:

class Datagram(BigEndianStructure):
_pack_ = 1
_fields_ = [
("MagicNumber", c_uint),
("VersionMinor", c_uint16),
("VersionMajor", c_uint16),
("SequenceNumber", c_uint16),
("SeqNumberHigh", c_uint16),
("DataSize", c_uint32),
("Attribute", GenericAttribute)
]


Why?

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