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pygatt - Python Module for Bluetooth LE Generic Attribute Profile (GATT).

This Module allows reading and writing to GATT descriptors on devices such as fitness trackers, sensors, and anything implementing standard GATT Descriptor behavior.

pygatt provides a Pythonic API by wrapping two different backends:

  • BlueZ (requires Linux), using the gatttool command-line utility.
  • Bluegiga's BGAPI, compatible with USB adapters like the BLED112.

Motivation

Despite the popularity of BLE, we have yet to find a good programming interface for it on desktop computers. Since most peripherals are designed to work with smartphones, this space is neglected. One interactive interface, BlueZ's gatttool, is functional but difficult to use programmatically. BlueZ itself obviously works, but the interface leaves something to be desired and only works in Linux.

Requirements

  • Python 2.7.5 or greater, or Python 3.5 or greater
    • Python 2.7.3's struct library has a bug that will break PyGATT - 2.7.5
      or greater is recommended.
  • BlueZ 5.18 or greater (with gatttool) - required for the gatttool backend only.
    • Tested on 5.18, 5.21, 5.35 and 5.43
  • GATTToolBackend requires Linux and sudo (i.e. not Windows compatible)

Installation

Install pygatt with pip from PyPI:

$ pip install pygatt

The BlueZ backend is not supported by default as it requires pexpect, which can only be installed in a UNIX-based environment. If you wish to use that backend, install the optional dependencies with:

$ pip install "pygatt[GATTTOOL]"

Install the latest development version of pygatt with pip:

$ pip install git+https://github.com/peplin/pygatt

Documentation

The documentation for pygatt consists of:

  • This README
  • The code in the samples directory
  • The Python docstrings in the code itself.

The BLEDevice and BLEBackend base classes are the primary interfaces for users of the library.

Known Issues

  • Performance has not been profiled, and there have been reports that both GATTTool and BGAPI backends struggled to handle high rate notifications (e.g. > 100Hz).
  • There is no way for the user to be notified if a device disconnects asynchronously (#306).
  • PIN-based authentication is not supported.
  • Duplicate characteristic names across different BLE service UUIDs are not supported.
  • Long characteristic reads and writes are only supported by the BGAPI backend.

Example Use

The primary API for users of this library is provided by pygatt.BLEBackend and pygatt.BLEDevice. After initializing an instance of the preferred backend (available implementations are found in pygatt.backends, use the BLEBackend.connect method to connect to a device and get an instance of BLEDevice.

import pygatt

# The BGAPI backend will attempt to auto-discover the serial device name of the
# attached BGAPI-compatible USB adapter.
adapter = pygatt.BGAPIBackend()

try:
    adapter.start()
    device = adapter.connect('01:23:45:67:89:ab')
    value = device.char_read("a1e8f5b1-696b-4e4c-87c6-69dfe0b0093b")
finally:
    adapter.stop()

Note that not all backends support connecting to more than 1 device at at time, so calling BLEBackend.connect again may terminate existing connections.

Here's the same example using the GATTTool backend. It's identical except for the initialization of the backend:

import pygatt

adapter = pygatt.GATTToolBackend()

try:
    adapter.start()
    device = adapter.connect('01:23:45:67:89:ab')
    value = device.char_read("a1e8f5b1-696b-4e4c-87c6-69dfe0b0093b")
finally:
    adapter.stop()

Notifications Example

This example uses the gatttool backend to connect to a device with a specific MAC address, subscribes for notifications on a characteristic, and prints the data returned in each notification.

import pygatt
from binascii import hexlify

adapter = pygatt.GATTToolBackend()

def handle_data(handle, value):
    """
    handle -- integer, characteristic read handle the data was received on
    value -- bytearray, the data returned in the notification
    """
    print("Received data: %s" % hexlify(value))

try:
    adapter.start()
    device = adapter.connect('01:23:45:67:89:ab')

    device.subscribe("a1e8f5b1-696b-4e4c-87c6-69dfe0b0093b",
                     callback=handle_data)

    # The subscription runs on a background thread. You must stop this main
    # thread from exiting, otherwise you will not receive any messages, and
    # the program will exit. Sleeping in a while loop like this is a simple
    # solution that won't eat up unnecessary CPU, but there are many other
    # ways to handle this in more complicated program. Multi-threaded
    # programming is outside the scope of this README.
    while True:
        time.sleep(10)
finally:
    adapter.stop()

Debugging

While debugging software using pygatt, it is often useful to see what's happening inside the library. You can enable debugging logging and have it printed to your terminal with this code:

import pygatt
import logging

logging.basicConfig()
logging.getLogger('pygatt').setLevel(logging.DEBUG)

Random Addressing

If you are having trouble connecting to a device, it may use random addressing. Try changing the connection setup code to:

device = adapter.connect('01:23:45:67:89:ab', address_type=pygatt.BLEAddressType.random)

Unexplained Timeouts

If you are experiencing unexplained timeouts with the gatttool backend, you may need to increase the supervisor timeouts:

echo 1000 > /sys/kernel/debug/bluetooth/hci0/supervision_timeout

Can't find BGAPI device in Windows

You may need to explicitly specify the COM port of your BGAPI-compatible device in windows, e.g.:

adapter = pygatt.BGAPIBackend(serial_port='COM9')

If you provide the COM port name, but still get an error such as WindowsError(2, 'The system cannot find the file specified.'), try changing the COM port of the device to a value under 10, e.g. COM9.

Authors

Releasing to PyPI

For the maintainers of the project, when you want to make a release:

  • Merge all of the changes into master.
  • Update the version in setup.py.
  • Update the CHANGELOG.mkd
  • Tag the commit and push to GitHub (will need to push to a separate branch of PR first since master is a protected branch).
  • Travis CI will take care of the rest - it will build and deploy tagged commits to PyPI automatically.

License

Copyright 2015 Stratos Inc. and Orion Labs

Apache License, Version 2.0 and MIT License. See LICENSE.

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Python wrapper for gatttool (a deprecated tool from BlueZ) and the BGAPI for accessing Bluetooth LE Devices

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