3.5. Advanced usage

3.5.1. Asynchronous device discovery

The device discovery and remote name request methods described earlier are both synchronous methods in that they don't return until the requests are complete, which can often taken a long time. During this time, the controlling thread blocks and can't do anything else, such as responding to user input or displaying other information. To avoid this, PyBluez provides the DeviceDiscoverer class for asynchronous device discovery and name lookup.

import bluetooth
import select

class MyDiscoverer(bluetooth.DeviceDiscoverer):
    
    def pre_inquiry(self):
        self.done = False
    
    def device_discovered(self, address, device_class, name):
        print "%s - %s" % (address, name)

    def inquiry_complete(self):
        self.done = True

d = MyDiscoverer()
d.find_devices(lookup_names = True)

readfiles = [ d, ]

while True:
    rfds = select.select( readfiles, [], [] )[0]

    if d in rfds:
        d.process_event()

    if d.done: break

To asynchronously detect nearby bluetooth devices, create a subclass of DeviceDiscoverer and override the pre_inquiry, device_discovered, and inquiry_complete methods. To start the discovery process, invoke find_devices, which returns immediately. pre_inquiry is called immediately before the actual inquiry process begins, and inquiry_complete is called as soon as the process completes.

MyDiscoverer exposes a fileno method, which allows it to be used with the select module. This provides a way for a single thread of control to wait for events on many open files at once, and greatly simplifies event-driven programs.

Call process_event to have the DeviceDiscoverer process pending events, which can be either a discovered device or the inquiry completion. When a nearby device is detected, device_discovered is invoked, with the address and device class of the detected device. If lookup_names was set in the call to find_devices, then name will also be set to the user-friendly name of the device. For more information about device classes, see https://www.bluetooth.org/foundry/assignnumb/document/baseband. The DeviceDiscoverer class can be used directly with the select module, and can easily be integrated into event loops of existing applications.

3.5.2. The _bluetooth module

The bluetooth module provides classes and utility functions useful for the most common Bluetooth programming tasks. More advanced functionality can be found in the _bluetooth extension module, which is little more than a thin wrapper around the BlueZ C API described in the next chapter. Lower level Bluetooth operations, such as establishing a connection with the actual Bluetooth microcontroller on the local machine and reading signal strength information, can be performed with the _bluetooth module in most cases without having to resort to the C API. An overview of the classes and methods available in _bluetooth is beyond the scope of this chapter, but the module documentation and examples are provided with the PyBluez distribution.