Question

I have a byte stream with 3 bytes that I have to cast into an unsigned int 32. In C I would just use bzero to zero out the memory region of my integer and then copy the memory from the stream, something like

char* stream = ...;
Uint32 myInt;
bzero(myInt,4);
memcopy(myInt, stream[0], stream[3])

Question:

How would I do this in Python?

Cheers

Answer 1

Even in C you should not use memcpy for binary de-serialization, because it doesn’t deal with binary representation, i.e. endianess, sign and the like. Explicitly decode binary values from a fixed representation in the stream to the platform’s native representation.

In Python, you’d read the bytes from the stream, pad them according to the endianess, and then unpack them with struct:

chunk = fileobj.read(3)
# decode bytes as little-endian, signed integer
chunk += '\x00'
number = struct.unpack('<i', chunk)

fileobj is a file-like object, representing the opened stream, i.e. a file opened with open(filename, 'rb').