You want an easy way to execute functions or methods in Python programs running onremote machines.
Perhaps the easiest way to implement a simple remote procedure call mechanism is touse XML-RPC. Here is an example of a simple server that implements a simple key-value store:
from xmlrpc.server import SimpleXMLRPCServer
class KeyValueServer:
_rpcmethods = [‘get', ‘set', ‘delete', ‘exists', ‘keys']def init(self, address):
self._data = {}self._serv = SimpleXMLRPCServer(address, allow_none=True)for name in self._rpcmethods:
self._serv.register_function(getattr(self, name))
def get(self, name):return self._data[name]def set(self, name, value):self._data[name] = valuedef delete(self, name):del self._data[name]def exists(self, name):return name in self._datadef keys(self):return list(self._data)def serve_forever(self):self._serv.serve_forever()
kvserv = KeyValueServer((‘', 15000))kvserv.serve_forever()
Here is how you would access the server remotely from a client:
>>> from xmlrpc.client import ServerProxy
>>> s = ServerProxy('http://localhost:15000', allow_none=True)
>>> s.set('foo', 'bar')
>>> s.set('spam', [1, 2, 3])
>>> s.keys()
['spam', 'foo']
>>> s.get('foo')
'bar'
>>> s.get('spam')
[1, 2, 3]
>>> s.delete('spam')
>>> s.exists('spam')
False
>>>XML-RPC can be an extremely easy way to set up a simple remote procedure call service.All you need to do is create a server instance, register functions with it using the register_function() method, and then launch it using the serve_forever() method. Thisrecipe packages it up into a class to put all of the code together, but there is no suchrequirement. For example, you could create a server by trying something like this:
from xmlrpc.server import SimpleXMLRPCServerdef add(x,y):
return x+y
serv = SimpleXMLRPCServer((‘', 15000))serv.register_function(add)serv.serve_forever()
Functions exposed via XML-RPC only work with certain kinds of data such as strings,numbers, lists, and dictionaries. For everything else, some study is required. For in‐stance, if you pass an instance through XML-RPC, only its instance dictionary ishandled:
>>> class Point:
... def __init__(self, x, y):
... self.x = x
... self.y = y
...
>>> p = Point(2, 3)
>>> s.set('foo', p)
>>> s.get('foo')
{'x': 2, 'y': 3}
>>>Similarly, handling of binary data is a bit different than you expect:
>>> s.set('foo', b'Hello World')
>>> s.get('foo')
<xmlrpc.client.Binary object at 0x10131d410>
>>> _.data
b'Hello World'
>>>As a general rule, you probably shouldn’t expose an XML-RPC service to the rest of theworld as a public API. It often works best on internal networks where you might wantto write simple distributed programs involving a few different machines.A downside to XML-RPC is its performance. The SimpleXMLRPCServer implementa‐tion is only single threaded, and wouldn’t be appropriate for scaling a large application,although it can be made to run multithreaded, as shown in Recipe 11.2. Also, sinceXML-RPC serializes all data as XML, it’s inherently slower than other approaches.However, one benefit of this encoding is that it’s understood by a variety of other pro‐gramming languages. By using it, clients written in languages other than Python will beable to access your service.Despite its limitations, XML-RPC is worth knowing about if you ever have the need tomake a quick and dirty remote procedure call system. Oftentimes, the simple solutionis good enough.