How to pack and unpack using ctypes (Structure <-> str)

Question

This might be a silly question but I couldn\'t find a good answer in the docs or anywhere.

If I use struct to define a binary structure, the struct

Answer 1

Have a look at this link on binary i/o in python:

http://www.dabeaz.com/blog/2009/08/python-binary-io-handling.html

Based on this you can simply write the following to read from a buffer (not just files):

g = open("foo","rb")
q = Example()
g.readinto(q)

To write is simply:

g.write(q)

The same for using sockets:

s.send(q)

and

s.recv_into(q)

I did some testing with pack/unpack and ctypes and this approach is the fastest except for writing straight in C

Answer 2

The PythonInfo wiki has a solution for this.

FAQ: How do I copy bytes to Python from a ctypes.Structure?

def send(self):
    return buffer(self)[:]

FAQ: How do I copy bytes to a ctypes.Structure from Python?

def receiveSome(self, bytes):
    fit = min(len(bytes), ctypes.sizeof(self))
    ctypes.memmove(ctypes.addressof(self), bytes, fit)

Their send is the (more-or-less) equivalent of pack, and receiveSome is sort of a pack_into. If you have a "safe" situation where you're unpacking into a struct of the same type as the original, you can one-line it like memmove(addressof(y), buffer(x)[:], sizeof(y)) to copy x into y. Of course, you'll probably have a variable as the second argument, rather than a literal packing of x.

Answer 3

Tested on Python3

e = Example(12, 13)
serialized = bytes(e)
deserialized = Example.from_buffer_copy(serialized)