Async Connections

Since the standard query() function is blocking, it can be a hazard for UI event loops. To deal with this, python-OBD has an Async connection object that can be used in place of the standard OBD object. Async is a subclass of OBD, and therefore inherits all of the standard methods. However, Async adds a few in order to control a threaded update loop. This loop will keep the values of your commands up to date with the vehicle. This way, when the user querys the car, the latest response is returned immediately.

The update loop is controlled by calling start() and stop(). To subscribe a command for updating, call watch() with your requested OBDCommand. Because the update loop is threaded, commands can only be watched while the loop is stoped.

General sequence to enable an asynchronous connection allowing non-blocking queries: - Async() # set-up the connection (to be used in place of OBD()) - watch() # add commands to the watch list - start() # start a thread performing the update loop in background - query() # perform the non-blocking query


import obd

connection = obd.Async() # same constructor as 'obd.OBD()'; see below. # keep track of the RPM

connection.start() # start the async update loop

print connection.query(obd.commands.RPM) # non-blocking, returns immediately

Callbacks can also be specified in watch(), and will return new Responses when available.

import obd
import time

connection = obd.Async()

# a callback that prints every new value to the console
def new_rpm(r):
    print (r.value), callback=new_rpm)

# the callback will now be fired upon receipt of new values


Async(portstr=None, baudrate=None, protocol=None, fast=True, timeout=0.1, check_voltage=True, delay_cmds=0.25)

Create asynchronous connection. Arguments are the same as 'obd.OBD()' with the addition of delay_cmds, which defaults to 0.25 seconds and allows controlling a delay after each loop executing all watched commands in background. If delay_cmds is set to 0, the background thread continuously repeats the execution of all commands without any delay.


Starts the update loop.


Stops the update loop.


A helper function for use in a Context Manager (a with statement) to temporarily stop the update loop. This makes it easy to protect your watch() and unwatch() calls. If the update loop was running at the time of being paused, it will be restarted upon exitting the context block. For instance:

with connection.paused() as was_running:
    # connection is stopped within this block
    # your code here

The code above is equivalent to:

was_running = connection.running

# your code here

if was_running:

watch(command, callback=None, force=False)

Note: The async loop must be stopped or paused before this function can be called

Subscribes a command to be continuously updated. After calling watch(), the query() function will return the latest Response from that command. An optional callback can also be set, and will be fired upon receipt of new values. Multiple callbacks for the same command are welcome. An optional force parameter will force an unsupported command to be sent.

unwatch(command, callback=None)

Note: The async loop must be stopped or paused before this function can be called

Unsubscribes a command from being updated. If no callback is specified, all callbacks for that command are dropped. If a callback is given, only that callback is unsubscribed (all others remain live).


Note: The async loop must be stopped or paused before this function can be called

Unsubscribes all commands and callbacks.