Counting bytes

[Fredrik Lundh]

Hugo Martires wrote:

> I need to send a list in a socket
>
> server side
> ------------
> list = [0.5 0.5 0.5 0.5]
> client.socket.send(list)

(did you try running this code?)

> client side
> -------------
> client.socket.recv(1024)
>
> the problem is the buffer size (1024 bytes)
> if i need to send a "big" list (with more than 1024 bytes), i have to count
> the number of bytes to send in parts. So i must know how many bytes my list
> oucupies.

a list contain objects, not bytes.  how things are stored in
memory is implementation dependent; unlike in C, there's no
way to get a pointer to the internal data structures.

to convert python objects to byte streams (and back), use
the pickle module (or cPickle or marshal).

    import pickle

    list = [0.5, 0.5, 0.5, 0.5]
    data = pickle.dumps(list)

    # data is now a string of bytes; use len(data) to
    # get the number of bytes

    list = pickle.loads(data)

more info here:

http://www.python.org/doc/current/lib/module-pickle.html

also see cPickle and marshal.  to produce an array of floating
point values (same as C's float data[] or double data[]), use
the array (or struct) module.

</F>

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