Operation Manual

Human-computer interfacing
119
Notes:
rpc_client.py:
importxmlrpc.client
s=xmlrpc.client.ServerProxy('http://localhost:8000')
# call the 'hello' function with no parameters
print(s. h e l l o())
# call the 'hello' function with a name
print(s.hello('XMLRPC'))
# add two numbers together
print('2+3=%s'%s.add(2,3))
To run this example, you need two separate IDLE windows – one for the server
and one for the client. You need to run the server first so that it is waiting for
requests from the client. To stop the server, press Ctrl-C.
How does it work? The server program sits and waits for requests from clients.
The client program, when run, calls the “hello” and “add” subroutines. The calls
are passed from the client to the server program, where the functions are actually
run. The result is then returned to the client program, which displays the result
on screen.
Where could this XMLRPC mechanism be used? Well, imagine that you have
several Raspberry Pis, each one connected to a screen located in a different
room. You also have a central computer running a control application with a
Graphical User Interface (GUI) designed to talk to every room over the network.
This central application could monitor and control every room by communicating
with individual Raspberry Pis – telling them what to display on the screen, control
devices via GPIO, and return data recorded from the room (such as light levels or
temperature). You could even take pictures with a camera! Each Raspberry Pi
would run as an XMLRPC server; the central control program would act as
the client.
Over to you
You can read more about Python’s XMLRPC modules here:
http://docs.python.org/py3k/library/xmlrpc.server.html
http://docs.python.org/py3k/library/xmlrpc.client.html
There are, however, XMLRPC libraries available in lots of other programming
languages.