zeroless 0.2.0

A pythonic approach for distributed systems with ZeroMQ.

Yet another ZeroMQ wrapper for Python. However, differing from pyzmq, which tries to stay very close to the C++ implementation, this project aims to make distributed systems employing 0MQ as pythonic as possible.

Being simpler to use, Zeroless doesn’t supports all of the fine aspects and features of 0MQ. However, you can expect to find all the message passing patterns you were accustomed to (i.e. pair, request/reply, publisher/subscriber, push/pull). Depite that, the only transport available is TCP, as threads are not as efficient in Python due to the GIL and IPC is unix-only.

Installation

$ pip install zeroless

Python API

In the zeroless module, two functions can be used to the define how zeroless’ sockets are related (i.e. bind and connect). Both are able to create a sort of generic 0MQ socket, which can then later become an instance of a specific message passing pattern.

The generic socket object is both callable and iterable. So that you can iterate over incoming messages, using the methods starting with listen_for_*, and/or call to transmit a message.

All examples assume:

from zeroless import (connect, bind)

Push-Pull

Useful for distributing the workload among a set of workers. A common pattern in the Stream Processing field, being the cornestone of applications like Apache Storm for instance. Also, it can be seen as a generalisation of the Map-Reduce pattern.

# The pull server binds to port 12345 and waits for incoming messages.
sock = bind(port=12345)

for msg in sock.listen_for_pull():
    print(msg)

# The push client connects to localhost and sends three messages.
sock = connect(port=12345)

for msg in ["Msg1", "Msg2", "Msg3"]:
    sock.push(msg.encode())

Publisher-Subscriber

Useful for broadcasting messages to a set of peers. A common pattern for allowing real-time notifications at the client side, without having to resort to inneficient approaches like pooling. Online services like PubNub or IoT protocols like MQTT are examples of this pattern usage.

# The subscriber server binds to port 12345 and waits for incoming messages.
sock = bind(port=12345)

for msg in sock.listen_for_pub():
    print(msg)

# The publisher client connects to localhost and sends three messages.
sock = connect(port=12345)

for msg in ["Msg1", "Msg2", "Msg3"]:
    sock.pub(msg.encode())

Note: There is no support for topic usage, as ZMQ’s topic filtering capabilities are client side only.

Request-Reply

Useful for RPC style calls. A common pattern for clients to request data and receive a response associated with the request. The HTTP protocol is well-known for adopting this pattern, being it essential for Restful services.

# The reply server binds to port 12345 and waits for incoming messages.
sock = bind(port=12345)

for msg in sock.listen_for_request():
    print(msg)
    sock.reply(msg)

# The request client connects to localhost and sends three messages.
sock = connect(port=12345)

for msg in ["Msg1", "Msg2", "Msg3"]:
    response = sock.request_and_listen(msg.encode())
    print(response)

Pair

More often than not, this pattern will be unnecessary, as the above ones or the mix of them suffices most use cases in distributed computing. Regarding its capabilities, this pattern is the most similar alternative to usual posix sockets among the aforementioned patterns. Therefore, expect one-to-one and bidirectional communication.

# The pair server binds to port 12345 and waits for incoming messages.
sock = bind(port=12345)

for msg in sock.listen_for_pair():
    print(msg)
    sock.pair(msg)

# The pair client connects to localhost and sends three messages.
sock = connect(port=12345)

for msg in ["Msg1", "Msg2", "Msg3"]:
    sock.pair(msg.encode())

Logging

The zeroless module allows logging via a global Logger object.

from zeroless import log

To enable it, just add an Handler object and set an appropriate logging level.

Testing

To run individual tests:

$ py.test tests/test_desired_module.py

To run all the tests:

$ python setup.py test

Alternatively, you can use tox:

$ tox

License

Copyright 2014 Lucas Lira Gomes [e-mail]

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library. If not, see http://www.gnu.org/licenses/.