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Using python with BT BLE

Note 1: although this guidelines are mostly for linux, I added an example at the end that should works on other systems

Note 2: we need a BLE compatible system. Please read bash.md

I use Oscar Acena gattlib (pygattlib) This library is also included in Piotr Karulis pybluez. Both libraries are included in ev3dev so we can use a LEGO MINDSTORMS EV3 to communicate with BT BLE devices. Of course, a BT BLE compatible device is needed, there are several USB dongles available.

For the record, there are at least two other libraries available:

pygatt seems very interesting because it also works outside Linux (but only with a smart BT BLE device). Unfortunately it is slow in linux since it makes system calls to gatttool instead of using BlueZ API directly like pygattlib does.

For a basic example, this is how we read the friendly name with python:

#!/usr/bin/env python3

from gattlib import GATTRequester

req = GATTRequester("00:16:53:A4:CD:7E",True,"hci0")
devicename=req.read_by_handle(0x07)
print(devicename[0])

I assume we just installed gattlib, so imported 'GATTRequester' directly from 'gattlib'. If we installed 'pybluez' with ble support instead, we should import it from 'bluetooth.ble':

from bluetooth.ble import GATTRequester

Please also note that handle '0x07' is the BLE handle associated to the "Device Name" characteristic for the current version of the LEGO BOOT firmware. Handles are not a property of the device, they are in fact the result of a discovery process of the characteristiscs of the device. So we really should have used 'read_by_uuid' instead of 'read_by_handle':

devicename=req.read_by_uuid("00002a00-0000-1000-8000-00805f9b34fb")

But as it is much more easy to remember a 2-char handle than a 32-char uuid I prefer to use the handle.

Some uuid's are already defined in a standard, so '2a00' is world wide used as the Device Name uuid. But other uuid's are used by some vendors for custom purposes that are not yet (and might never be) part of the BLE standard so these uuid's can change - LEGO developers may decide, in a future version of the firmware, that instead of using just one characteristic for all motors/sensors/RGB LED functions it's better to split it in several characteristics.

So don't take anything for granted. Specially if written by me :)

Now if you're using pygatt in l inux instead of pygattlib, here is the same example:

#!/usr/bin/env python3

import pygatt
adapter = pygatt.GATTToolBackend()

try:
    adapter.start()
    device = adapter.connect('00:16:53:A4:CD:7E')
    devicename = device.char_read_handle(0x07)
    print(devicename.decode("utf-8"))
    
finally:
    adapter.stop()

On non-linux systems, if you have a smart BT BLE device like the BLED112, just change the backend, using the BlueGiga instead of the GATTTool:

    adapter = pygatt.BGAPIBackend()