# select

This module provides functions to wait for events on streams \(select streams which are ready for operations\).

## Pyboard specifics

Polling is an efficient way of waiting for read/write activity on multiple objects. Current objects that support polling are: `pyb.UART`, `pyb.USB_VCP`.

## Methods

#### select.poll\(\)

Create an instance of the `Poll` class.

#### select.select\(rlist, wlist, xlist\[, timeout\]\)

Wait for activity on a set of objects.

This function is provided for compatibility and is not efficient. Usage of `Poll` is recommended instead.

## class Poll

### Methods

#### poll.register\(obj\[, eventmask\]\)

Register `obj` for polling. `eventmask` is logical OR of:

* `select.POLLIN` - data available for reading
* `select.POLLOUT` - more data can be written
* `select.POLLERR` - error occurred
* `select.POLLHUP` - end of stream/connection termination detected

  `eventmask` defaults to `select.POLLIN | select.POLLOUT`.

#### poll.unregister\(obj\)

Unregister `obj` from polling.

#### poll.modify\(obj, eventmask\)

Modify the `eventmask` for `obj`.

#### poll.poll\(\[timeout\]\)

Wait for at least one of the registered objects to become ready. Returns list of \(`obj`, `event`, ...\) tuples, `event` element specifies which events happened with a stream and is a combination of `select.POLL*` constants described above. There may be other elements in tuple, depending on a platform and version, so don’t assume that its size is 2. In case of timeout, an empty list is returned.

Timeout is in milliseconds.