selectors2 1.1.1

Drop-in replacement of the selectors module for Python 2.6+ that integrates PEP 475

Drop-in replacement of the selectors module for Python 2.6+ that integrates PEP 475.

• Support for all major platforms. (Linux, Mac OS, Windows)

• Support many different selectors

  • select.kqueue (BSD, Mac OS)

  • select.devpoll (Solaris)

  • select.epoll (Linux 2.5.44+)

  • select.poll (Linux, Mac OS)

  • select.select - (Linux, Mac OS, Windows)

• Support for PEP 475 (Retries syscalls on interrupt)

About

This module was originally written by me for the urllib3 project (history in PR #1001) but it was decided that it would be beneficial for everyone to have access to this work.

Can this module be used in place of selectors?

Yes! This module is a 1-to-1 drop-in replacement for selectors and provides all selector types that would be available in selectors including DevpollSelector, KqueueSelector, EpollSelector, PollSelector, and SelectSelector.

What is different between selectors2 and selectors34?

This module is similar to selectors34 in that it supports Python 2.6 - 3.3 but differs in that this module also implements PEP 475 for the backported selectors. This allows similar behaviour between Python 3.5+ selectors and selectors from before PEP 475. In selectors34, an interrupted system call would result in an incorrect return of no events, which for some use cases is not an acceptable behavior.

I will also add here that selectors2 also makes large improvements on the test suite surrounding it providing 100% test coverage for each selector. The test suite is also more robust and tests durability of the selectors in many different situations that aren’t tested in selectors34.

What types of objects are supported?

At this current time selectors2 only support the SelectSelector for Windows which cannot select on non-socket objects. On Linux and Mac OS, both sockets and pipes are supported (some other types may be supported as well, such as fifos or special file devices).

What if I have to support a platform without select.select?

There are a few platforms that don’t have a selector available, notably Google AppEngine, but there are probably a lot more. If you must support these platforms, one should check selectors.HAS_SELECTOR for a True value before trying to use selectors.DefaultSelector. Note this is not available for selectors or selectors34.

Windows has IOCP, why don’t you support it?

Yes, Windows has access to IOCP which is more performant than SelectSelector but is also much harder to implement and requires the win32 module to expose the interface. This is something I would like in the future, feel free to send a PR! :)

License

This module is dual-licensed under MIT and PSF License.

Installation

$ python -m pip install selectors2

Usage

import sys
if sys.version_info > (3, 5):  # Python 3.5+
    import selectors
else:  # Python 2.6 - 3.4
    import selectors2 as selectors

# Use DefaultSelector, it picks the fastest
# selector available for your platform! :)
s = selectors.DefaultSelector()

import socket

# We're going to use Google as an example.
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect(("www.google.com", 80))

# Register the file to be watched for write availibility.
s.register(sock, selectors.EVENT_WRITE)

# Give a timeout in seconds or no
# timeout to block until an event happens.
events = s.select(timeout=1.0)

# Loop over all events that happened.
for key, event in events:
    if event & selectors.EVENT_WRITE:
        key.fileobj.send(b'HEAD / HTTP/1.1\r\n\r\n')

# Change what event you're waiting for.
s.modify(sock, selectors.EVENT_READ)

# Timeout of None let's the selector wait as long as it needs to.
events = s.select(timeout=None)
for key, event in events:
    if event & selectors.EVENT_READ:
        data = key.fileobj.recv(4096)
        print(data)

# Stop watching the socket.
s.unregister(sock)
sock.close()

Contributing

This repository is thankful for all community-made PRs and Issues. :)

If this work is useful to you, feel free to say thanks, takes only a little time and really brightens my day! :cake:

Changelog

Release 1.1.1 (February 6, 2017)

• Platforms that define select.kqueue would not have KqueueSelector as the DefaultSelector.

Release 1.1.0 (January 17, 2017)

• Make system calls faster for Python versions that support PEP 475.

• Wheels are now universal.

Release 1.0.0 (November 3, 2016)

• Initial implementation of selectors2.