Invoking a class method from a Linux process which is a python script

There's no easy way to do that unless you have code in the server to also give you access to an interpreter while it's running, or on launching it.

EDIT: This "manhole" library looks promising for your use case, though like the other ideas listed it does require some modification of the server code to implement.

Is this code you wrote? If so, you could modify it to run the server in a background thread, and then use the code module to launch an interactive interpreter on the console with the appropriate modules/class instances (if needed) accessible. This only works for debugging, since this effectively turns your noninteractive server into an interactive Python process that happens to run a server in the background.

The Twisted library supported a telnet or SSH-based manhole feature, where you could essentially shell into the running Python process at any time, but integrating Twisted into a non-Twisted code base is not worth the trouble for this feature. I think there've been other implementations of this concept, including some that provide fancy HTML/JS interfaces, but I don't have the names/links handy.

This is exactly the problem that DBus solves. It allows you to invoke methods from another process.

I had asked a question about creating Hello World server using DBus, Register a "Hello World" DBus service, object and method using Python.

This is how the code for the server looks:

import gobject
import dbus
import dbus.service

from dbus.mainloop.glib import DBusGMainLoop
DBusGMainLoop(set_as_default=True)


OPATH = "/com/example/HelloWorld"
IFACE = "com.example.HelloWorld"
BUS_NAME = "com.example.HelloWorld"


class Example(dbus.service.Object):
    def __init__(self):
        bus = dbus.SessionBus()
        bus.request_name(BUS_NAME)
        bus_name = dbus.service.BusName(BUS_NAME, bus=bus)
        dbus.service.Object.__init__(self, bus_name, OPATH)

    @dbus.service.method(dbus_interface=IFACE + ".SayHello",
                         in_signature="", out_signature="")
    def SayHello(self):
        print "hello, world"


if __name__ == "__main__":
    a = Example()
    loop = gobject.MainLoop()
    loop.run()

And you can use dbus-send to call it.