.. module:: uselect :synopsis: wait for events on a set of streams
|see_cpython_module| :mod:`python:select`.
This module provides functions to efficiently wait for events on multiple streams <stream> (select streams which are ready for operations).
.. function:: poll() Create an instance of the Poll class.
.. function:: select(rlist, wlist, xlist[, timeout]) Wait for activity on a set of objects. This function is provided by some MicroPython ports for compatibility and is not efficient. Usage of :class:`Poll` is recommended instead.
Poll
.. method:: poll.register(obj[, eventmask]) Register `stream` *obj* for polling. *eventmask* is logical OR of: * ``uselect.POLLIN`` - data available for reading * ``uselect.POLLOUT`` - more data can be written Note that flags like ``uselect.POLLHUP`` and ``uselect.POLLERR`` are *not* valid as input eventmask (these are unsolicited events which will be returned from `poll()` regardless of whether they are asked for). This semantics is per POSIX. *eventmask* defaults to ``uselect.POLLIN | uselect.POLLOUT``. It is OK to call this function multiple times for the same *obj*. Successive calls will update *obj*'s eventmask to the value of *eventmask* (i.e. will behave as `modify()`).
.. method:: poll.unregister(obj) Unregister *obj* from polling.
.. method:: poll.modify(obj, eventmask) Modify the *eventmask* for *obj*. If *obj* is not registered, `OSError` is raised with error of ENOENT.
.. method:: poll.poll(timeout=-1, /) Wait for at least one of the registered objects to become ready or have an exceptional condition, with optional timeout in milliseconds (if *timeout* arg is not specified or -1, there is no timeout). Returns list of (``obj``, ``event``, ...) tuples. There may be other elements in tuple, depending on a platform and version, so don't assume that its size is 2. The ``event`` element specifies which events happened with a stream and is a combination of ``uselect.POLL*`` constants described above. Note that flags ``uselect.POLLHUP`` and ``uselect.POLLERR`` can be returned at any time (even if were not asked for), and must be acted on accordingly (the corresponding stream unregistered from poll and likely closed), because otherwise all further invocations of `poll()` may return immediately with these flags set for this stream again. In case of timeout, an empty list is returned. .. admonition:: Difference to CPython :class: attention Tuples returned may contain more than 2 elements as described above.
.. method:: poll.ipoll(timeout=-1, flags=0, /) Like :meth:`poll.poll`, but instead returns an iterator which yields a `callee-owned tuple`. This function provides an efficient, allocation-free way to poll on streams. If *flags* is 1, one-shot behavior for events is employed: streams for which events happened will have their event masks automatically reset (equivalent to ``poll.modify(obj, 0)``), so new events for such a stream won't be processed until new mask is set with `poll.modify()`. This behavior is useful for asynchronous I/O schedulers. .. admonition:: Difference to CPython :class: attention This function is a MicroPython extension.
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