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+:mod:`selectors` --- High-level I/O multiplexing
+================================================
+
+.. module:: selectors
+   :synopsis: High-level I/O multiplexing.
+
+.. versionadded:: 3.4
+
+**Source code:** :source:`Lib/selectors.py`
+
+--------------
+
+Introduction
+------------
+
+This module allows high-level and efficient I/O multiplexing, built upon the
+:mod:`select` module primitives. Users are encouraged to use this module
+instead, unless they want precise control over the OS-level primitives used.
+
+It defines a :class:`BaseSelector` abstract base class, along with several
+concrete implementations (:class:`KqueueSelector`, :class:`EpollSelector`...),
+that can be used to wait for I/O readiness notification on multiple file
+objects. In the following, "file object" refers to any object with a
+:meth:`fileno()` method, or a raw file descriptor. See :term:`file object`.
+
+:class:`DefaultSelector` is an alias to the most efficient implementation
+available on the current platform: this should be the default choice for most
+users.
+
+.. note::
+   The type of file objects supported depends on the platform: on Windows,
+   sockets are supported, but not pipes, whereas on Unix, both are supported
+   (some other types may be supported as well, such as fifos or special file
+   devices).
+
+.. seealso::
+
+   :mod:`select`
+      Low-level I/O multiplexing module.
+
+
+Classes
+-------
+
+Classes hierarchy::
+
+   BaseSelector
+   +-- SelectSelector
+   +-- PollSelector
+   +-- EpollSelector
+   +-- DevpollSelector
+   +-- KqueueSelector
+
+
+In the following, *events* is a bitwise mask indicating which I/O events should
+be waited for on a given file object. It can be a combination of the modules
+constants below:
+
+   +-----------------------+-----------------------------------------------+
+   | Constant              | Meaning                                       |
+   +=======================+===============================================+
+   | :const:`EVENT_READ`   | Available for read                            |
+   +-----------------------+-----------------------------------------------+
+   | :const:`EVENT_WRITE`  | Available for write                           |
+   +-----------------------+-----------------------------------------------+
+
+
+.. class:: SelectorKey
+
+   A :class:`SelectorKey` is a :class:`~collections.namedtuple` used to
+   associate a file object to its underlying file descriptor, selected event
+   mask and attached data. It is returned by several :class:`BaseSelector`
+   methods.
+
+   .. attribute:: fileobj
+
+      File object registered.
+
+   .. attribute:: fd
+
+      Underlying file descriptor.
+
+   .. attribute:: events
+
+      Events that must be waited for on this file object.
+
+   .. attribute:: data
+
+      Optional opaque data associated to this file object: for example, this
+      could be used to store a per-client session ID.
+
+
+.. class:: BaseSelector
+
+   A :class:`BaseSelector` is used to wait for I/O event readiness on multiple
+   file objects. It supports file stream registration, unregistration, and a
+   method to wait for I/O events on those streams, with an optional timeout.
+   It's an abstract base class, so cannot be instantiated. Use
+   :class:`DefaultSelector` instead, or one of :class:`SelectSelector`,
+   :class:`KqueueSelector` etc. if you want to specifically use an
+   implementation, and your platform supports it.
+   :class:`BaseSelector` and its concrete implementations support the
+   :term:`context manager` protocol.
+
+   .. abstractmethod:: register(fileobj, events, data=None)
+
+      Register a file object for selection, monitoring it for I/O events.
+
+      *fileobj* is the file object to monitor.  It may either be an integer
+      file descriptor or an object with a ``fileno()`` method.
+      *events* is a bitwise mask of events to monitor.
+      *data* is an opaque object.
+
+      This returns a new :class:`SelectorKey` instance, or raises a
+      :exc:`ValueError` in case of invalid event mask or file descriptor, or
+      :exc:`KeyError` if the file object is already registered.
+
+   .. abstractmethod:: unregister(fileobj)
+
+      Unregister a file object from selection, removing it from monitoring. A
+      file object shall be unregistered prior to being closed.
+
+      *fileobj* must be a file object previously registered.
+
+      This returns the associated :class:`SelectorKey` instance, or raises a
+      :exc:`KeyError` if *fileobj* is not registered.  It will raise
+      :exc:`ValueError` if *fileobj* is invalid (e.g. it has no ``fileno()``
+      method or its ``fileno()`` method has an invalid return value).
+
+   .. method:: modify(fileobj, events, data=None)
+
+      Change a registered file object's monitored events or attached data.
+
+      This is equivalent to :meth:`BaseSelector.unregister(fileobj)` followed
+      by :meth:`BaseSelector.register(fileobj, events, data)`, except that it
+      can be implemented more efficiently.
+
+      This returns a new :class:`SelectorKey` instance, or raises a
+      :exc:`ValueError` in case of invalid event mask or file descriptor, or
+      :exc:`KeyError` if the file object is not registered.
+
+   .. abstractmethod:: select(timeout=None)
+
+      Wait until some registered file objects become ready, or the timeout
+      expires.
+
+      If ``timeout > 0``, this specifies the maximum wait time, in seconds.
+      If ``timeout <= 0``, the call won't block, and will report the currently
+      ready file objects.
+      If *timeout* is ``None``, the call will block until a monitored file object
+      becomes ready.
+
+      This returns a list of ``(key, events)`` tuples, one for each ready file
+      object.
+
+      *key* is the :class:`SelectorKey` instance corresponding to a ready file
+      object.
+      *events* is a bitmask of events ready on this file object.
+
+      .. note::
+          This method can return before any file object becomes ready or the
+          timeout has elapsed if the current process receives a signal: in this
+          case, an empty list will be returned.
+
+      .. versionchanged:: 3.5
+         The selector is now retried with a recomputed timeout when interrupted
+         by a signal if the signal handler did not raise an exception (see
+         :pep:`475` for the rationale), instead of returning an empty list
+         of events before the timeout.
+
+   .. method:: close()
+
+      Close the selector.
+
+      This must be called to make sure that any underlying resource is freed.
+      The selector shall not be used once it has been closed.
+
+   .. method:: get_key(fileobj)
+
+      Return the key associated with a registered file object.
+
+      This returns the :class:`SelectorKey` instance associated to this file
+      object, or raises :exc:`KeyError` if the file object is not registered.
+
+   .. abstractmethod:: get_map()
+
+      Return a mapping of file objects to selector keys.
+
+      This returns a :class:`~collections.abc.Mapping` instance mapping
+      registered file objects to their associated :class:`SelectorKey`
+      instance.
+
+
+.. class:: DefaultSelector()
+
+   The default selector class, using the most efficient implementation
+   available on the current platform. This should be the default choice for
+   most users.
+
+
+.. class:: SelectSelector()
+
+   :func:`select.select`-based selector.
+
+
+.. class:: PollSelector()
+
+   :func:`select.poll`-based selector.
+
+
+.. class:: EpollSelector()
+
+   :func:`select.epoll`-based selector.
+
+   .. method:: fileno()
+
+      This returns the file descriptor used by the underlying
+      :func:`select.epoll` object.
+
+.. class:: DevpollSelector()
+
+   :func:`select.devpoll`-based selector.
+
+   .. method:: fileno()
+
+      This returns the file descriptor used by the underlying
+      :func:`select.devpoll` object.
+
+   .. versionadded:: 3.5
+
+.. class:: KqueueSelector()
+
+   :func:`select.kqueue`-based selector.
+
+   .. method:: fileno()
+
+      This returns the file descriptor used by the underlying
+      :func:`select.kqueue` object.
+
+
+Examples
+--------
+
+Here is a simple echo server implementation::
+
+   import selectors
+   import socket
+
+   sel = selectors.DefaultSelector()
+
+   def accept(sock, mask):
+       conn, addr = sock.accept()  # Should be ready
+       print('accepted', conn, 'from', addr)
+       conn.setblocking(False)
+       sel.register(conn, selectors.EVENT_READ, read)
+
+   def read(conn, mask):
+       data = conn.recv(1000)  # Should be ready
+       if data:
+           print('echoing', repr(data), 'to', conn)
+           conn.send(data)  # Hope it won't block
+       else:
+           print('closing', conn)
+           sel.unregister(conn)
+           conn.close()
+
+   sock = socket.socket()
+   sock.bind(('localhost', 1234))
+   sock.listen(100)
+   sock.setblocking(False)
+   sel.register(sock, selectors.EVENT_READ, accept)
+
+   while True:
+       events = sel.select()
+       for key, mask in events:
+           callback = key.data
+           callback(key.fileobj, mask)