how to send objects through python?

Question

I have a server:

import socket
import time
import random
from PIL import ImageGrab

server_socket = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
server_socket.bind(('127.0.0.1',8820))
server_socket.listen(1)

while True:
    print "Waiting for commands"
    a = ImageGrab.grab()
    CommandDict = {"TIME" : time.strftime("%a %b %d %H:%M:%S %Y"),"NAME": "Ori","RANDOM":   str(random.randint(0,10)),"EXIT":"BYE","PRINT SCREEN":a}
    (client_socket, client_address) = server_socket.accept()
    client_data = client_socket.recv(1024)
    print "GOT COMMAND FROM " + client_address[0] + " : " + client_data
    client_socket.send(CommandDict[client_data])
    client_socket.close()

server_socket.close()

and the client:

import socket
from PIL import ImageGrab
while True:
    client_input = raw_input("Enter You Command: ")
    CommandList=["EXIT","TIME","NAME","RANDOM","PRINT SCREEN"]
    if client_input in CommandList:
        my_socket=socket.socket()
        my_socket.connect(('127.0.0.1',8820))
        my_socket.send(client_input)
        data = my_socket.recv(1024) + "\n"
        if client_input=="PRINT SCREEN":
        data.save()
        else:
            print "SERVER: " + data
    else: 
        print "Invalid command. try one of those: " + " , ".join(CommandList) + "\n" + "."


my_socket.close()

When i try this it gives me an error because it trys to send it as a string object. I want to send an object through socket and i want the client to read it. Any ideas?

In this server it's an image object but I want to know a way to send all kinds of objects. — oridamari, Dec 18 '14 at 08:51
You need to serialize the objects before you send them. On the receiving end you restore the objects. — Andreas Argelius, Dec 18 '14 at 08:53
Have a look at https://docs.python.org/2/library/pickle.html#module-pickle — Dunes, Dec 18 '14 at 09:00
You can send them by serializing them into JSON format. See [_Making object JSON serializable with regular encoder_](http://stackoverflow.com/questions/18478287/making-object-json-serializable-with-regular-encoder). — martineau, Dec 18 '14 at 09:02

score 2 · Answer 1 · answered Dec 18 '14 at 09:00

2

Python includes an object serialization module called pickle: https://docs.python.org/2/library/pickle.html

You can use pickle.dumps(CommandDict[client_data]) to produce a string which you can then send on a socket. Then use pickle.loads to restore the object on the other side. Of course this requires that the object is "pickleable", but many simple data structures are, or can be made so without much trouble. In your case you may need to add some code to pickle the ImageGrab object type, but try it first and see if it works by default.

answered Dec 18 '14 at 09:00

John Zwinck

239,568
38
324
436

2

No need to create the string (which will be fairly large as it represents an image in some instances). The following will have better performance: `f = my_socket.makefile(); pickle.dump(CommandDict[client_data], f)`. – Dunes Dec 18 '14 at 09:07
2

It should be pointed out that if `pickle` is used, the server will have to be able to access the source code for the pickled object(s) in order to reconstitute it or them back into their original form. – martineau Dec 18 '14 at 09:10
@Dunes: thank you for pointing that out, I had thought that should be possible but didn't know offhand exactly how. – John Zwinck Dec 18 '14 at 09:15
I tried to pickle the ImageGrab i and it didnt work, how can i do it? Is there a way to send "unpickleable" objects? – oridamari Dec 18 '14 at 09:18
1

@oridamari You will need to register a function that knows how to pickle and perhaps unpickle the object. See the [copy_reg](https://docs.python.org/2/library/copy_reg.html#module-copy_reg) module. – Dunes Dec 18 '14 at 09:41

Dunes · Answer 2 · 2014-12-19T09:06:02.197

The following should allow you to pickle an image. I don't have PIL on my current machine, so I haven't been able to test it properly. The machine

import cPickle as pickle # cPickle is considerably more efficient than pickle
import copy_reg
from StringIO import StringIO
from PIL import Image, ImageGrab

def pickle_image(img):
    """Turns an image into a data stream. Only required on machine sending the 
    image."""
    data = StringIO()
    img.save(data, 'png')
    data.seek(0)
    return unpickle_image, (data,)

def unpickle_image(data):
   """Turns a data stream into an image. Required on both machines"""
    img = Image.open(data)
    data.close() # releases internal buffer immediately
    return img

# tells pickle it should use the function pickle_image to pickle objects of 
# type Image. Required on the machine sending the image
copy_reg.pickle(Image, pickle_image)

some_image = ImageGrab.grab()
# HIGHEST_PROTOCOL uses a more effcient representation of the object
pickled_image = pickle.dumps(some_image, pickle.HIGHEST_PROTOCOL)

unpickled_image = pickle.loads(pickled_image)

In my code I have used dumps and loads to create and use a string representation of the data. Ideally you should be using dump and load, passing my_socket.makefile() as the file argument.

how to send objects through python?

2 Answers2

Linked