PYRO - Example

Pyro Manual

8. Example

In this chapter you'll find a short but complete example that shows how Pyro must be used and how it works. However, much more interesting examples can be found in the examples directory. For the real impatient people, I recommend the "quickstart" example, because you'll see that you can eliminate very much of the (already little!) extra work you have to do to make a Pyro application.

(Note: the example below is from Pyro 1.5 on Linux)

Write a module 'test.py' containing a class 'testclass', which will be accessed remotely.

class testclass:
    def mul(s, arg1, arg2): return arg1*arg2
    def add(s, arg1, arg2): return arg1+arg2
    def sub(s, arg1, arg2): return arg1-arg2
    def div(s, arg1, arg2): return arg1/arg2
    def error(s): raise ValueError('Server generated exception, this is ok!')

Using PyroC, generate client proxy code for 'testclass'. You can skip this part if you use the Dynamic Proxy in step 5.

irmen@atlantis:~/Pyro/test > pyroc test
Python Remote Object Compiler (c) Irmen de Jong. Pyro V1.5

[added current directory to import path]
processing module 'test' (/home/irmen/Pyro-1_5/test/test.py)...
examining class testclass ...
Generating proxy for testclass
This release of Pyro doesn't need server-side skeleton code.

All done. Output can be found in test_proxy.py .

Write a server, testserver.py, that creates one or more instances of the 'testclass', and registers them with the Pyro Naming Service.

import sys, socket
import Pyro.naming
import Pyro.core
from Pyro.errors import PyroError,NamingError

import test

###### testclass Pyro object

class testclass(Pyro.core.ObjBase, test.testclass):
	pass

###### main server program

def main():
	Pyro.core.initServer()
	# locate the NS
	PyroDaemon = Pyro.core.Daemon()
	locator = Pyro.naming.NameServerLocator()
	print 'searching for Naming Service...'
	try:
		ns = locator.getNS()
	except (PyroError,socket.error),x:
		hn = socket.gethostname()
		print '\nNaming Service not found with broadcast. Trying host',hn,'...',
		ns = locator.getNS(host=hn)

	print 'Naming Service found at',ns.URI.address,'('+(Pyro.protocol.getHostname(ns.URI.address) or '??')+') port',ns.URI.port

	PyroDaemon.useNameServer(ns)

	# connect a new object implementation (first unregister previous one)
	try:
		ns.unregister('test')
	except NamingError:
		pass

	# connect new object implementation
	PyroDaemon.connect(testclass(),'test')

	# enter the server loop.
	print 'Server object "test" ready.'
	while 1:
		PyroDaemon.handleRequests(3.0)
		sys.stdout.write('.')
		sys.stdout.flush()

if __name__=="__main__":
	main()

Write a client, testclient.py, that will find the Naming Service.

import sys, socket
import Pyro.naming, Pyro.core

# look for static proxy
try:
        import test_proxy
        print '*** Using static test_proxy.'
        dynproxy = 0
except ImportError:
        print '*** No static test_proxy found. Using dynamic proxy.'
        dynproxy = 1

Pyro.core.initClient()

# locate the NS
locator = Pyro.naming.NameServerLocator()
print 'Searching Naming Service...',
try:
        ns = locator.getNS()
except (Pyro.core.PyroError, socket.error),x:
        hn = socket.gethostname()
        print '\nNaming Service not found with broadcast. Trying host',hn,'...',
        ns = locator.getNS(host=hn)

print 'Naming Service found at',ns.URI.address,'('+(Pyro.protocol.getHostname(ns.URI.address) or '??')+') port',ns.URI.port

(... continued ...)

Let the client query the NS for the object's URI. Then create a proxy for the remote object by creating a 'test_proxy.testclass' instance for the given URI, or creating a Dynamic Proxy for the URI. Because the proxy appears the same as the real 'testclass', the client can now invoke methods on the remote objects.

(...continued from above...)

# resolve the Pyro object
print 'binding to object'
try:
        URI=ns.resolve('test')
        print 'URI:',URI
except Pyro.core.PyroError,x:
        print 'Couldn\'t bind object, nameserver says:',x
        raise SystemExit

# create a proxy for the Pyro object, and return that
if dynproxy:
        # use dynamic proxy
        test = Pyro.core.getProxyForURI(URI)
else:
        # use static (precompiled) proxy
        test = test_proxy.testclass(URI)

print test.mul(111,9)
print test.add(100,222)
print test.sub(222,100)
print test.div(2.0,9.0)
print test.mul('*',10)
print test.add('String1','String2')
print '*** Now a server-generated exception should occur:'
print test.error()

Run the application in the network. First, start the Naming Service on one computer.

irmen@atlantis:~ > ns
Pyro Server Initialized. Using Pyro V1.5
Will accept shutdown requests.
URI written to: /home/irmen/Pyro_NS_URI
URI is: PYRO://192.168.0.99:9090/c0a80063-16d55032-c784739a-45067dfb
Naming Service started.

Start the server on another computer (or in a different shell).

irmen@atlantis:~/Pyro/test > python testserver.py 
Pyro Server Initialized. Using Pyro V1.5
searching for Naming Service...
Naming Service found at 192.168.0.99 (atlantis.home.nl) port 9090
Server object "test" ready.
......

Finally, run the client on a third computer (or in a different shell).

irmen@atlantis:~/Pyro/test > python testclient.py
*** Using static test_proxy.
Pyro Client Initialized. Using Pyro V1.5
Searching Naming Service... Naming Service found at 192.168.0.99 (atlantis.home.nl) port 9090
binding to object
URI: PYRO://192.168.0.99:7766/c0a80063-14ff5033-d7de73e1-150f1c0d
999
322
122
0.222222222222
**********
String1String2
*** Now a server-generated exception should occur:
Traceback (most recent call last):
  File "testclient.py", line 51, in ?
    print test.error()
  File "test_proxy.py", line 32, in error
    return S.adapter.remoteInvocation('error',0)
  File "/home/irmen/Pyro/Pyro/protocol.py", line 151, in remoteInvocation
    answer.raiseEx()
  File "/home/irmen/Pyro/Pyro/errors.py", line 50, in raiseEx
    raise self.excObj
ValueError: Server generated exception, this is ok!

You might want to peek in the Naming Server:

irmen@atlantis:~/Pyro/test > nsc listall
Finding NS using broadcast @ port 9091
LOCATOR: Searching Pyro Naming Service...
NS is at 192.168.0.99 (atlantis.home.nl) port 9090
-------------- START DATABASE
:Default.test  -->  PYRO://192.168.0.99:7766/c0a80063-14ff5033-d7de73e1-150f1c0d
:Pyro.NameServer  -->  PYRO://192.168.0.99:9090/c0a80063-16d55032-c784739a-45067dfb
-------------- END

And if you're interested you may want to try the logging facility of Pyro. First, set the tracelevel to something other than the default, 0. See the chapter on configuration how to do that. Usually you'll set the environment variable PYRO_TRACELEVEL to 3 (=maximum logging). Then, when you start Pyro programs (like the nameserver), they will write something like this to the logfile:

------------------------------------------------------------ NEW SESSION
Thu Jan 18 14:14:15 2001   Pyro Initializing, version 1.5
This is initServer.
Configuration settings are as follows:
PYRO_BC_RETRIES = 2
PYRO_BC_TIMEOUT = 2
PYRO_BINARY_PICKLE = 1
PYRO_COMPRESSION = 0
PYRO_CONFIG_FILE = 
PYRO_LOGFILE = /home/irmen/Pyro_log
PYRO_MAXCONNECTIONS = 200
PYRO_MULTITHREADED = 1
PYRO_NS_BC_PORT = 9091
PYRO_NS_DEFAULTGROUP = :Default
PYRO_NS_GROUPSEP = .
PYRO_NS_NAME = :Pyro.NameServer
PYRO_NS_PORT = 9090
PYRO_NS_ROOTCHAR = :
PYRO_NS_URIFILE = /home/irmen/Pyro_NS_URI
PYRO_PORT = 7766
PYRO_PORT_RANGE = 100
PYRO_STORAGE = /home/irmen
PYRO_TRACELEVEL = 3
PYRO_USER_LOGFILE = /home/irmen/Pyro_userlog
PYRO_USER_TRACELEVEL = 0
Init done.
----------------------------------------------------------------------
01/18/01 14:14:15 ** NOTE ** PYROAdapter ** adapter daemon set to <Pyro Daemon on atlantis:9999>
01/18/01 14:14:15 ** NOTE ** NameServer ** created group :Pyro
01/18/01 14:14:15 ** NOTE ** NameServer ** created group :Default
01/18/01 14:14:15 ** NOTE ** NameServer ** registered NameServer with URI PYRO://192.168.0.99:9999/c0a80063-4e065034-3f78dae8-2d3fdc85
01/18/01 14:14:15 ** NOTE ** NameServer ** URI written to /home/irmen/Pyro_NS_URI
01/18/01 14:14:15 ** NOTE ** NS daemon ** This is Pyro Naming Service V1.4.
01/18/01 14:14:15 ** NOTE ** NS daemon ** Starting on atlantis port 9999  broadcast server on port 9091