python-message-0.1.0

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python-messagepython-messagea message-oriented programming librarya message-oriented programming library

Lai YonghaoLai Yonghao

http://laiyonghao.comhttp://laiyonghao.com

2010.12.192010.12.19

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outline

technical background

examples

features and APIs

brief introduction

implementation

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outline

technical background

examples

features and APIs

brief introduction

implementation

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python-message is ...

• a python publish-subscribe broker for messages within an application (NOT network).

• inspired by falcon languagesubscribe("printl", {tbp => >tbp})broadcast("printl", "Hello world!")

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home

• http://pypi.python.org/pypi/message• http://code.google.com/p/python-message/

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installation

• easy_install message

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usage

import messagedef hello(context, name): print 'hello, %s.'%namemessage.sub('greet', hello)message.pub('greet', 'lai')

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outline

technical background

examples

features and APIs

brief introduction

implementation

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message-oriented programming

• Message-oriented programming (MOP) consists in writing program sections generating and replying to messages (happening now, in the future or even happened in the past) instead of writing direct calls.

• A message is formed by a topic and zero or more parameters.

• from Falcon wiki

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publish-subscribe pattern

• Publish/subscribe (or pub/sub) is a messaging pattern where senders (publishers) of messages do not program the messages to be sent directly to specific receivers (subscribers).

• This decoupling of publishers and subscribers can allow for greater scalability.

• The observer pattern is a subset of the publish-subscribe pattern.

• from wikipedia

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outline

technical background

examples

features and APIs

brief introduction

implementation

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features

• the topic is NOT exclusively a string, all Hashable item can be used

• pub() is performed synchronously, the order by which handlers are called is the same order in which they have subscribed

• set context.discontinued = True in listerner function to interrupte publish

• listeners can unsubscribe from listening messages and declarations through the unsub() function

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APIs

• sub/unsub• pub• declare/retract• get_declarations/has_declaration

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sub/unsub

• sub(topic, listener, front = False)• unsub(topic, listener)

– topic:Hashable– listener:Callable, def listener(context, *a, **k):pass– front:put listener on top of the listeners list, default is F

alse

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pub

• pub(topic, *a, **k)– topic:Hashable– a and k:parameters will be posted to the listener(s)

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declare/retract, etc.

• declare(topic, *a, *k)– topic:Hashable– announce topic– calls all listeners– if a topic is declared, sub(topic, listener) invokes listen

er immediately

• retract(topic)– removes an existing declaration

• get_declarations()• has_declaration(topic)

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outline

technical background

examples

features and APIs

brief introduction

implementation

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examples

• decoupling logging from your library• dancing with process/thread/coroutine

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decoupling logging from your library(1)

# before# foo.pylogger = logging.getLogger("prjA")def bar(): logger.debug(txt) do_sth()

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decoupling logging from your library(2)

# afterimport messageLOG_MSG = ('log', 'foo')def bar(): messeage.pub(LOG_MSG, 'Haha, Calling

bar().') do_sth()

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decoupling logging from your library(3)

import logginglogger = logging.getLogger("prjA")def handle_foo_log_msg(ctx, txt): logger.debug(txt)

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decoupling logging from your library(4)

def handle_foo_log_msg(ctx, txt): import logging logging.debug(txt)

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decoupling logging from your library(5)

import messageimport foodef handle_foo_log_msg(ctx, txt): print txtmessage.sub(foo.LOG_MSG,

handle_foo_log_msg)

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dancing with process/thread/coroutine

• all you need is a decorate function

@new_XXXdef listener(context, *a, **k): do_sth()

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dancing with process

from multiprocessing import Processfrom functools import wrapsdef new_process(func): @wraps(func) def _func(*a, **k): p = Process(target = func, args = a, kwargs = k) p.start() return _func

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dancing with thread

from threading import Threadfrom functools import wrapsdef new_thread(func): @wraps(func) def _func(*a, **k): p = Thread(target = func, args = a, kwargs = k) p.start() return _func

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dancing with coroutine(greenlet)

from greenlet import greenletfrom functools import wrapsdef new_greenlet(func): @wraps(func) def _func(*a, **k): p = greenlet(func, *a, **k) p.start() return _func

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outline

technical background

examples

features and APIs

brief introduction

implementation

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Talk is cheap. Show me the code.Talk is cheap. Show me the code.

Linus Torvalds

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This is not the end, This is not the end, this is just the beginning.this is just the beginning.

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reference

• http://en.wikipedia.org/wiki/Message_passing• http://en.wikipedia.org/wiki/Publish/subscribe• http://en.wikipedia.org/wiki/Observer_pattern• http://pubsub.sourceforge.net/• http://falconpl.org/index.ftd?

page_id=sitewiki&prj_id=_falcon_site&sid=wiki&pwid=Survival+Guide&wid=Survival%3AMessage+oriented+programming

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Thank you !Thank you !

@laiyonghao@laiyonghao