Python in a Nutshell

Name

select

Synopsis

select(inputs,outputs,excepts,timeout=None)

inputs, outputs, and excepts are lists of socket objects waiting for input events, output events, and exceptional conditions, respectively. timeout is a float, the maximum time to wait in seconds. When timeout is None, there is no maximum wait: select waits until one or more objects receive events. When timeout is 0, select returns at once, without waiting.

select returns a tuple with three items ( i,o,e ). i is a list of zero or more of the items of inputs, those that received input events. o is a list of zero or more of the items of outputs, those that received output events. e is a list of zero or more of the items of excepts, those that received exceptional conditions (i.e., out-of-band data). Any or all of i, o, and e can be empty, but at least one of them is non-empty if timeout is None.

In addition to sockets, you can have in lists inputs, outputs, and excepts other objects that supply a method fileno, callable without arguments, returning a socket’s file descriptor. For example, the server classes of module SocketServer, covered earlier in this chapter, follow this protocol. Therefore, you can have instances of those classes in the lists. On Unix-like platforms, select.select has wider applicability, since it can also accept file descriptors that do not refer to sockets. On Windows, however, select.select can accept only file descriptors that do refer to sockets.

Example 19-6 uses module select to reimplement ...