Publish/Subscribe
#!/usr/bin/env python
#
# [SNIPPET_NAME: Publish/Subscribe]
# [SNIPPET_CATEGORIES: Patterns, PyGTK]
# [SNIPPET_DESCRIPTION: A module providing a minimal implementation of the Publish/Subscribe Pattern]
# [SNIPPET_AUTHOR: Bastian Kennel <[email protected]>]
# [SNIPPET_LICENSE: GPL]
"""This Pattern is very useful for communication between indepentdent parts of a program."""
# wikipedia: http://en.wikipedia.org/wiki/Publish/subscribe
import gtk
import logging
subscriptions = {}
def subscribe(message, subscriber):
"""
Subscribes the subscriber to a message. Subscriber has to be callable and
accept all parameters the message issues.
Message can be anything, but should be a primitive (like a string) to not
complicate subscriber implementations.
"""
if not message in subscriptions:
subscriptions[message] = [subscriber]
else:
subscriptions[message].append(subscriber)
def publish(message, *args, **kwargs):
"""
Publish a message with respective arguments.
Call every subscriber to this message and pass the arguments.
"""
if not message in subscriptions:
logging.info("Message with no Subscribers: " + str(message))
return
for subscriber in subscriptions[message]:
try:
subscriber(*args, **kwargs)
except Exception, e:
logging.error("Subscriber " + str(subscriber) + " could not handle message " + str(message) + ": " + str(args) + str(kwargs))
def unsubscribe(message, subscriber):
"""Unsubscribe the subscriber from the message."""
if not message in subscriptions:
logging.info("No Message to unsibscribe from: " + str(message))
elif not subscriber in subscriptions[message]:
logging.info("Subscriber " + str(subscriber) + " not subscribed for message " + str(message))
else:
subscriptions[message].remove(subscriber)
# # # # Example Code from here on # # # #
# example taken from the python-snippet 'Buttons'
import pygtk
pygtk.require('2.0')
import gtk
def xpm_label_box(parent, xpm_filename, label_text):
# Create box for xpm and label
box1 = gtk.HBox(False, 0)
box1.set_border_width(2)
# Now on to the image stuff
image = gtk.Image()
image.set_from_file(xpm_filename)
# Create a label for the button
label = gtk.Label(label_text)
# Pack the pixmap and label into the box
box1.pack_start(image, False, False, 3)
box1.pack_start(label, False, False, 3)
image.show()
label.show()
return box1
# the message to communicate with
MESSAGE = "THE_message"
# dumb subscription stub
def someFunctionAnywhereDoingAnything(some, data, optional=42):
print "I received ", some, data, " along with optional ", optional
class Buttons:
# Our usual callback method
def callback(self, widget, data=None):
print "Hello again - %s was pressed" % data
# publishing
publish(MESSAGE, "an", " invitation", optional = "nothing.")
def __init__(self):
# Create a new window
self.window = gtk.Window(gtk.WINDOW_TOPLEVEL)
self.window.set_title("Image'd Buttons!")
# It's a good idea to do this for all windows.
self.window.connect("destroy", lambda wid: gtk.main_quit())
self.window.connect("delete_event", lambda a1,a2:gtk.main_quit())
# Sets the border width of the window.
self.window.set_border_width(10)
# Create a new button
button = gtk.Button()
# Connect the "clicked" signal of the button to our callback
button.connect("clicked", self.callback, "cool button")
# This calls our box creating function
box1 = xpm_label_box(self.window, "info.xpm", "cool button")
# Pack and show all our widgets
button.add(box1)
box1.show()
button.show()
self.window.add(button)
self.window.show()
def main():
# subscribing
subscribe(MESSAGE, someFunctionAnywhereDoingAnything)
gtk.main()
return 0
if __name__ == "__main__":
Buttons()
main()