multiprocessing Listeners and Clients between python and pypy
Question: Is it possible to have a [Listener server process and a Client
process](http://docs.python.org/library/multiprocessing.html#module-
multiprocessing.connection) where one of them uses a python interpreter and
the other a [pypy](http://pypy.org/) interpreter?

Would `conn.send()` and `conn.recv()` interoperate well?


Answer: I tried it out to see:

    
    
    import sys
    from multiprocessing.connection import Listener, Client
    
    address = ('localhost', 6000)
    
    def client():
        conn = Client(address, authkey='secret password')
        print conn.recv_bytes()
        conn.close()
    
    def server():
        listener = Listener(address, authkey='secret password')
        conn = listener.accept()
        print 'connection accepted from', listener.last_accepted
        conn.send_bytes('hello')
        conn.close()
        listener.close()
    
    if __name__ == '__main__':
        if sys.argv[1] == 'client':
            client()
        else:
            server()
    

Here are the results I got:

  * CPython 2.7 + CPython 2.7: **working**
  * PyPy 1.7 + PyPy 1.7: **working**
  * CPython 2.7 + PyPy 1.7: **not working**
  * CPython 2.7 + PyPy Nightly (pypy-c-jit-50911-94e9969b5f00-linux64): **working**

When using PyPy 1.7 (doesn't matter which is the server and which is the
client), an error is reported with `IOError: bad message length`. This also
mirrors [the report on the pypy-dev mailing list](http://www.mail-
archive.com/pypy-dev@python.org/msg01607.html). However, this was recently
fixed (it works in nightly build), so the next version (presumably 1.8) should
have it fixed as well.

In general, this works because the multiprocessing module uses Python's
[pickle](http://docs.python.org/library/pickle.html) module, which is stable
and supported across multiple Python implementations, even PyPy.

