Implementation of select.poll on Microsoft Windows.

• Pure Python; no C extensions (uses ctypes.windll.Ws2_32)
• Drop-in-compatible API
• Clean "ponyfill"; library does no monkeypatching
• Python 3.7+ compatible
• No dependencies

Usage

Alternative to select.poll

try:
    from select import (
        POLLIN, POLLOUT, POLLERR, POLLHUP, POLLNVAL,
        poll
    )

except ImportError:
    # https://github.com/python/cpython/issues/60711
    from winpoll import (
        POLLIN, POLLOUT, POLLERR, POLLHUP, POLLNVAL,
        wsapoll as poll
    )

p = poll()

p.register(sock1, POLLIN)
p.register(sock2, POLLIN | POLLOUT)
p.unregister(sock1)

for fd, events in p.poll(3):
    print(f"<socket.socket fd={fd}> is ready with {events}")

Like select.poll, winpoll.wsapoll objects acquire no special resources, thus have no cleanup requirement (besides plain garbage collection).

Alternative to selectors.PollSelector/selectors.DefaultSelector

import sys
from selectors import (
    EVENT_READ, EVENT_WRITE,
    DefaultSelector, SelectSelector
)

if (DefaultSelector is SelectSelector) and (sys.platform == 'win32') and (sys.getwindowsversion() >= (10, 0, 19041)):
    # https://github.com/python/cpython/issues/60711
    from winpoll import WSAPollSelector as DefaultSelector

s = DefaultSelector()

s.register(sock1, EVENT_READ)
s.register(sock2, EVENT_READ | EVENT_WRITE)
s.unregister(sock1)

for (sock, _fd, _eventmask, _data), events in s.select(3):
    print(f"{sock} is ready with {events}")

Limitations / Bugs

• Does not work before Windows Vista.

  • Last affected OS: Windows XP (EOL April 8, 2014; not supported by Python 3.7+ anyway.)

• Outbound TCP connections don't correctly report failure-to-connect ((POLLHUP | POLLERR | POLLWRNORM)) before Windows 10 version 2004 ("May 2020 Update" / "20H1" / "OS Build 19041").

  • Last affected OS: Windows 10 version 1909 (EOL May 10, 2022.)

Installation

Command-line

pip install "winpoll ; sys_platform == 'win32'"

requirements.txt

...
winpoll ; sys_platform == 'win32'

setup.py

...

setup(
    ...,
    install_requires: [
        ...,
        "winpoll ; sys_platform == 'win32'"
    ]
)

pyproject.toml

[project]
...

dependencies = [
  ...,
  "winpoll ; sys_platform == 'win32'",
]